fs/splice: don't block splice_direct_to_actor() after data was read

  From: Max Kellermann <max.kellermann@ionos.com>

If userspace calls sendfile() with a very large "count" parameter, the
kernel can block for a very long time until 2 GiB (0x7ffff000 bytes)
have been read from the hard disk and pushed into the socket buffer.

Usually, that is not a problem, because the socket write buffer gets
filled quickly, and if the socket is non-blocking, the last
direct_splice_actor() call will return -EAGAIN, causing
splice_direct_to_actor() to break from the loop, and sendfile() will
return a partial transfer.

However, if the network happens to be faster than the hard disk, and
the socket buffer keeps getting drained between two
generic_file_read_iter() calls, the sendfile() system call can keep
running for a long time, blocking for disk I/O over and over.

That is undesirable, because it can block the calling process for too
long.  I discovered a problem where nginx would block for so long that
it would drop the HTTP connection because the kernel had just
transferred 2 GiB in one call, and the HTTP socket was not writable
(EPOLLOUT) for more than 60 seconds, resulting in a timeout:

  sendfile(4, 12, [5518919528] => [5884939344], 1813448856) = 366019816 <3.033067>
  sendfile(4, 12, [5884939344], 1447429040) = -1 EAGAIN (Resource temporarily unavailable) <0.000037>
  epoll_wait(9, [{EPOLLOUT, {u32=2181955104, u64=140572166585888}}], 512, 60000) = 1 <0.003355>
  gettimeofday({tv_sec=1667508799, tv_usec=201201}, NULL) = 0 <0.000024>
  sendfile(4, 12, [5884939344] => [8032418896], 2147480496) = 2147479552 <10.727970>
  writev(4, [], 0) = 0 <0.000439>
  epoll_wait(9, [], 512, 60000) = 0 <60.060430>
  gettimeofday({tv_sec=1667508869, tv_usec=991046}, NULL) = 0 <0.000078>
  write(5, "10.40.5.23 - - [03/Nov/2022:21:5"..., 124) = 124 <0.001097>
  close(12) = 0 <0.000063>
  close(4)  = 0 <0.000091>

In newer nginx versions (since 1.21.4), this problem was worked around
by defaulting "sendfile_max_chunk" to 2 MiB:

 https://github.com/nginx/nginx/commit/5636e7f7b4

Instead of asking userspace to provide an artificial upper limit, I'd
like the kernel to block for disk I/O at most once, and then pass back
control to userspace.

There is prior art for this kind of behavior in filemap_read():

	/*
	 * If we've already successfully copied some data, then we
	 * can no longer safely return -EIOCBQUEUED. Hence mark
	 * an async read NOWAIT at that point.
	 */
	if ((iocb->ki_flags & IOCB_WAITQ) && already_read)
		iocb->ki_flags |= IOCB_NOWAIT;

This modifies the caller-provided "struct kiocb", which has an effect
on repeated filemap_read() calls.  This effect however vanishes
because the "struct kiocb" is not persistent; splice_direct_to_actor()
doesn't have one, and each generic_file_splice_read() call initializes
a new one, losing the "IOCB_NOWAIT" flag that was injected by
filemap_read().

There was no way to make generic_file_splice_read() aware that
IOCB_NOWAIT was desired because some data had already been transferred
in a previous call:

- checking whether the input file has O_NONBLOCK doesn't work because
  this should be fixed even if the input file is not non-blocking

- the SPLICE_F_NONBLOCK flag is not appropriate because it affects
  only whether pipe operations are non-blocking, not whether
  file/socket operations are non-blocking

Since there are no other parameters, I suggest adding the
SPLICE_F_NOWAIT flag, which is similar to SPLICE_F_NONBLOCK, but
affects the "non-pipe" file descriptor passed to sendfile() or
splice().  It translates to IOCB_NOWAIT for regular files.  For now, I
have documented the flag to be kernel-internal with a high bit, like
io_uring does with SPLICE_F_FD_IN_FIXED, but making this part of the
system call ABI may be a good idea as well.

To: Alexander Viro <viro@zeniv.linux.org.uk>
To: linux-fsdevel@vger.kernel.org
To: linux-kernel@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---
 fs/splice.c            | 14 ++++++++++++++
 include/linux/splice.h |  6 ++++++
 2 files changed, 20 insertions(+)
  

On Sat, Nov 05, 2022 at 10:04:21AM +0100, Max Kellermann wrote:
> Since there are no other parameters, I suggest adding the
> SPLICE_F_NOWAIT flag, which is similar to SPLICE_F_NONBLOCK, but
> affects the "non-pipe" file descriptor passed to sendfile() or
> splice().  It translates to IOCB_NOWAIT for regular files.

This looks reasonable to me and matches the read/write side.

>
> For now, I
> have documented the flag to be kernel-internal with a high bit, like
> io_uring does with SPLICE_F_FD_IN_FIXED, but making this part of the
> system call ABI may be a good idea as well.

Yeah, my only comment here is that I see no reason to make this
purely kernel internal.

And while looking at that: does anyone remember why the (public)
SPLICE_F_* aren't in a uapi header?
  

Greeting,

FYI, we noticed a 3388.6% improvement of phoronix-test-suite.stress-ng.SENDFILE.bogo_ops_s due to commit:

commit: 86f00c46806e19ccce7fa238fbf3aaf0f1f2f531 ("[PATCH] fs/splice: don't block splice_direct_to_actor() after data was read")
url: https://github.com/intel-lab-lkp/linux/commits/Max-Kellermann/fs-splice-don-t-block-splice_direct_to_actor-after-data-was-read/20221105-171212
base: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git b208b9fbbcba743fb269d15cb46a4036b01936b1
patch link: https://lore.kernel.org/all/20221105090421.21237-1-mk@cm4all.com/
patch subject: [PATCH] fs/splice: don't block splice_direct_to_actor() after data was read

in testcase: phoronix-test-suite
on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz (Cascade Lake) with 512G memory
with following parameters:

	test: stress-ng-1.3.1
	option_a: SENDFILE
	cpufreq_governor: performance

test-description: The Phoronix Test Suite is the most comprehensive testing and benchmarking platform available that provides an extensible framework for which new tests can be easily added.
test-url: http://www.phoronix-test-suite.com/


Details are as below:

=========================================================================================
compiler/cpufreq_governor/kconfig/option_a/rootfs/tbox_group/test/testcase:
  gcc-11/performance/x86_64-rhel-8.3/SENDFILE/debian-x86_64-phoronix/lkp-csl-2sp7/stress-ng-1.3.1/phoronix-test-suite

commit: 
  b208b9fbbc ("Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux")
  86f00c4680 ("fs/splice: don't block splice_direct_to_actor() after data was read")

b208b9fbbcba743f 86f00c46806e19ccce7fa238fbf 
---------------- --------------------------- 
         %stddev     %change         %stddev
             \          |                \  
    105881 ± 10%   +3388.6%    3693772 ± 13%  phoronix-test-suite.stress-ng.SENDFILE.bogo_ops_s
      2.16 ±  7%   +1117.6%      26.36 ± 13%  phoronix-test-suite.time.user_time
      0.20            +0.2        0.40 ±  4%  mpstat.cpu.all.usr%
     97.92 ±  6%     +14.9%     112.48 ±  5%  sched_debug.cfs_rq:/.util_est_enqueued.stddev
      2717            +2.5%       2783        turbostat.Bzy_MHz
    254.74            -4.6%     243.11        turbostat.PkgWatt
   2589095 ± 18%     -37.5%    1617492 ± 28%  numa-meminfo.node0.FilePages
    788063 ± 62%    +123.2%    1758697 ± 26%  numa-meminfo.node1.FilePages
    992948 ± 48%     +92.6%    1912574 ± 24%  numa-meminfo.node1.Inactive
   1803548 ± 28%     +52.3%    2746365 ± 17%  numa-meminfo.node1.MemUsed
 4.443e+09 ± 12%     -36.0%  2.846e+09 ± 18%  numa-numastat.node0.local_node
 4.429e+09 ± 12%     -35.8%  2.842e+09 ± 18%  numa-numastat.node0.numa_hit
 5.558e+09 ±  8%     -54.2%  2.548e+09 ± 24%  numa-numastat.node1.local_node
 5.539e+09 ±  8%     -54.0%  2.545e+09 ± 24%  numa-numastat.node1.numa_hit
 9.968e+09 ± 10%     -46.0%  5.388e+09 ± 13%  proc-vmstat.numa_hit
     1e+10 ± 10%     -46.1%  5.393e+09 ± 13%  proc-vmstat.numa_local
 9.759e+09 ± 10%     -45.5%   5.32e+09 ± 13%  proc-vmstat.pgalloc_normal
 9.759e+09 ± 10%     -45.5%   5.32e+09 ± 13%  proc-vmstat.pgfree
    647020 ± 19%     -37.5%     404382 ± 28%  numa-vmstat.node0.nr_file_pages
 4.429e+09 ± 12%     -35.8%  2.842e+09 ± 18%  numa-vmstat.node0.numa_hit
 4.443e+09 ± 12%     -36.0%  2.846e+09 ± 18%  numa-vmstat.node0.numa_local
    196897 ± 62%    +123.3%     439599 ± 26%  numa-vmstat.node1.nr_file_pages
 5.539e+09 ±  8%     -54.0%  2.545e+09 ± 24%  numa-vmstat.node1.numa_hit
 5.558e+09 ±  8%     -54.2%  2.548e+09 ± 24%  numa-vmstat.node1.numa_local
 2.602e+10 ± 10%     -39.6%  1.573e+10 ± 13%  perf-stat.i.branch-instructions
  24921395 ± 12%     +40.0%   34894184 ±  6%  perf-stat.i.branch-misses
 1.223e+08 ± 11%     -37.8%   76029198 ± 13%  perf-stat.i.cache-references
      1.92 ± 18%     +43.1%       2.75 ± 12%  perf-stat.i.cpi
  2.05e+11            +2.6%  2.103e+11        perf-stat.i.cpu-cycles
 3.522e+10 ± 10%     -37.8%  2.192e+10 ± 13%  perf-stat.i.dTLB-loads
 2.356e+10 ± 10%     -40.7%  1.396e+10 ± 13%  perf-stat.i.dTLB-stores
   2507922 ± 14%    +527.4%   15734908 ±  8%  perf-stat.i.iTLB-load-misses
 1.336e+11 ± 10%     -39.6%  8.071e+10 ± 13%  perf-stat.i.instructions
     50055 ± 12%     -90.8%       4589 ±  5%  perf-stat.i.instructions-per-iTLB-miss
      0.61 ± 10%     -35.9%       0.39 ± 10%  perf-stat.i.ipc
   2135130            +2.7%    2191818        perf-stat.i.metric.GHz
 8.845e+08 ± 10%     -39.1%  5.387e+08 ± 13%  perf-stat.i.metric.M/sec
     60647 ±  2%     -19.8%      48635 ±  6%  perf-stat.i.node-stores
      0.10 ±  8%      +0.1        0.22 ±  7%  perf-stat.overall.branch-miss-rate%
     11.06 ± 35%      +5.9       16.96 ± 25%  perf-stat.overall.cache-miss-rate%
      1.55 ± 12%     +70.3%       2.65 ± 11%  perf-stat.overall.cpi
      0.00 ± 41%      +0.0        0.00 ± 29%  perf-stat.overall.dTLB-store-miss-rate%
     86.38 ±  3%     +10.8       97.16        perf-stat.overall.iTLB-load-miss-rate%
     53972 ± 12%     -90.5%       5111 ±  5%  perf-stat.overall.instructions-per-iTLB-miss
      0.65 ± 11%     -41.2%       0.38 ± 12%  perf-stat.overall.ipc
 2.579e+10 ± 10%     -39.5%  1.559e+10 ± 13%  perf-stat.ps.branch-instructions
  24705183 ± 12%     +40.1%   34602922 ±  6%  perf-stat.ps.branch-misses
 1.212e+08 ± 11%     -37.8%   75385416 ± 13%  perf-stat.ps.cache-references
 2.032e+11            +2.6%  2.085e+11        perf-stat.ps.cpu-cycles
 3.491e+10 ± 10%     -37.7%  2.173e+10 ± 13%  perf-stat.ps.dTLB-loads
 2.335e+10 ± 10%     -40.7%  1.385e+10 ± 13%  perf-stat.ps.dTLB-stores
   2486067 ± 14%    +527.6%   15601840 ±  8%  perf-stat.ps.iTLB-load-misses
 1.324e+11 ± 10%     -39.5%  8.002e+10 ± 13%  perf-stat.ps.instructions
     60175 ±  2%     -19.8%      48272 ±  6%  perf-stat.ps.node-stores
 1.529e+13 ± 10%     -39.5%  9.254e+12 ± 12%  perf-stat.total.instructions
     55.97 ±  6%     -13.5       42.46 ±  4%  perf-profile.calltrace.cycles-pp.do_iter_readv_writev.do_iter_read.ovl_read_iter.generic_file_splice_read.splice_direct_to_actor
     55.59 ±  6%     -13.4       42.15 ±  4%  perf-profile.calltrace.cycles-pp.shmem_file_read_iter.do_iter_readv_writev.do_iter_read.ovl_read_iter.generic_file_splice_read
     29.58 ± 11%     -12.7       16.90 ± 12%  perf-profile.calltrace.cycles-pp.iov_iter_zero.shmem_file_read_iter.do_iter_readv_writev.do_iter_read.ovl_read_iter
     57.68 ±  3%     -11.7       45.98        perf-profile.calltrace.cycles-pp.do_iter_read.ovl_read_iter.generic_file_splice_read.splice_direct_to_actor.do_splice_direct
     17.32 ± 12%      -7.4        9.89 ± 14%  perf-profile.calltrace.cycles-pp.append_pipe.iov_iter_zero.shmem_file_read_iter.do_iter_readv_writev.do_iter_read
     13.20 ± 12%      -5.5        7.66 ± 15%  perf-profile.calltrace.cycles-pp.__alloc_pages.append_pipe.iov_iter_zero.shmem_file_read_iter.do_iter_readv_writev
     10.88 ± 11%      -4.6        6.27 ±  9%  perf-profile.calltrace.cycles-pp.memset_erms.iov_iter_zero.shmem_file_read_iter.do_iter_readv_writev.do_iter_read
     15.34 ±  7%      -4.3       11.02 ± 14%  perf-profile.calltrace.cycles-pp.direct_splice_actor.splice_direct_to_actor.do_splice_direct.do_sendfile.__x64_sys_sendfile64
     15.23 ±  7%      -4.3       10.96 ± 14%  perf-profile.calltrace.cycles-pp.splice_from_pipe.direct_splice_actor.splice_direct_to_actor.do_splice_direct.do_sendfile
     15.05 ±  7%      -4.2       10.86 ± 14%  perf-profile.calltrace.cycles-pp.__splice_from_pipe.splice_from_pipe.direct_splice_actor.splice_direct_to_actor.do_splice_direct
      8.26 ± 11%      -3.2        5.06 ± 14%  perf-profile.calltrace.cycles-pp.get_page_from_freelist.__alloc_pages.append_pipe.iov_iter_zero.shmem_file_read_iter
      8.38 ±  9%      -2.4        6.01 ± 14%  perf-profile.calltrace.cycles-pp.free_unref_page.__splice_from_pipe.splice_from_pipe.direct_splice_actor.splice_direct_to_actor
      5.64 ± 10%      -1.9        3.70 ± 13%  perf-profile.calltrace.cycles-pp.rmqueue.get_page_from_freelist.__alloc_pages.append_pipe.iov_iter_zero
     99.74            -1.5       98.21        perf-profile.calltrace.cycles-pp.splice_direct_to_actor.do_splice_direct.do_sendfile.__x64_sys_sendfile64.do_syscall_64
     99.75            -1.4       98.36        perf-profile.calltrace.cycles-pp.do_splice_direct.do_sendfile.__x64_sys_sendfile64.do_syscall_64.entry_SYSCALL_64_after_hwframe
      2.30 ± 13%      -1.1        1.20 ± 16%  perf-profile.calltrace.cycles-pp.alloc_pages.append_pipe.iov_iter_zero.shmem_file_read_iter.do_iter_readv_writev
      1.74 ± 12%      -0.8        0.96 ± 11%  perf-profile.calltrace.cycles-pp.xas_load.__filemap_get_folio.shmem_get_folio_gfp.shmem_file_read_iter.do_iter_readv_writev
     99.79            -0.8       99.03        perf-profile.calltrace.cycles-pp.do_sendfile.__x64_sys_sendfile64.do_syscall_64.entry_SYSCALL_64_after_hwframe
      1.52 ± 12%      -0.7        0.79 ± 15%  perf-profile.calltrace.cycles-pp.free_unref_page_commit.free_unref_page.__splice_from_pipe.splice_from_pipe.direct_splice_actor
      4.13 ±  3%      -0.7        3.46 ± 13%  perf-profile.calltrace.cycles-pp.generic_pipe_buf_release.__splice_from_pipe.splice_from_pipe.direct_splice_actor.splice_direct_to_actor
      1.01 ± 11%      -0.6        0.40 ± 72%  perf-profile.calltrace.cycles-pp.free_pcp_prepare.free_unref_page.__splice_from_pipe.splice_from_pipe.direct_splice_actor
     99.80            -0.4       99.36        perf-profile.calltrace.cycles-pp.__x64_sys_sendfile64.do_syscall_64.entry_SYSCALL_64_after_hwframe
     99.82            -0.4       99.47        perf-profile.calltrace.cycles-pp.do_syscall_64.entry_SYSCALL_64_after_hwframe
      0.79 ± 10%      -0.3        0.48 ± 45%  perf-profile.calltrace.cycles-pp.__list_del_entry_valid.rmqueue.get_page_from_freelist.__alloc_pages.append_pipe
      0.90 ±  7%      -0.3        0.59 ±  4%  perf-profile.calltrace.cycles-pp.__might_resched.shmem_file_read_iter.do_iter_readv_writev.do_iter_read.ovl_read_iter
     99.83            -0.3       99.52        perf-profile.calltrace.cycles-pp.entry_SYSCALL_64_after_hwframe
     83.75            +2.5       86.27 ±  2%  perf-profile.calltrace.cycles-pp.generic_file_splice_read.splice_direct_to_actor.do_splice_direct.do_sendfile.__x64_sys_sendfile64
     83.42            +2.5       85.97 ±  2%  perf-profile.calltrace.cycles-pp.ovl_read_iter.generic_file_splice_read.splice_direct_to_actor.do_splice_direct.do_sendfile
     11.81 ± 13%      +6.4       18.22        perf-profile.calltrace.cycles-pp.override_creds.ovl_read_iter.generic_file_splice_read.splice_direct_to_actor.do_splice_direct
     13.34 ± 14%      +7.7       21.02 ±  7%  perf-profile.calltrace.cycles-pp.revert_creds.ovl_read_iter.generic_file_splice_read.splice_direct_to_actor.do_splice_direct
     55.98 ±  6%     -13.5       42.46 ±  4%  perf-profile.children.cycles-pp.do_iter_readv_writev
     55.85 ±  6%     -13.5       42.34 ±  4%  perf-profile.children.cycles-pp.shmem_file_read_iter
     29.70 ± 11%     -12.7       16.96 ± 12%  perf-profile.children.cycles-pp.iov_iter_zero
     57.69 ±  3%     -11.7       45.98        perf-profile.children.cycles-pp.do_iter_read
     17.38 ± 12%      -7.5        9.93 ± 14%  perf-profile.children.cycles-pp.append_pipe
     13.64 ± 12%      -5.7        7.90 ± 15%  perf-profile.children.cycles-pp.__alloc_pages
     10.94 ± 10%      -4.6        6.30 ±  9%  perf-profile.children.cycles-pp.memset_erms
     15.34 ±  7%      -4.3       11.02 ± 14%  perf-profile.children.cycles-pp.direct_splice_actor
     15.24 ±  7%      -4.3       10.96 ± 14%  perf-profile.children.cycles-pp.splice_from_pipe
     15.13 ±  7%      -4.2       10.90 ± 14%  perf-profile.children.cycles-pp.__splice_from_pipe
      8.36 ± 11%      -3.2        5.11 ± 14%  perf-profile.children.cycles-pp.get_page_from_freelist
      8.62 ±  9%      -2.5        6.13 ± 14%  perf-profile.children.cycles-pp.free_unref_page
      5.76 ± 10%      -2.0        3.76 ± 13%  perf-profile.children.cycles-pp.rmqueue
     99.74            -1.5       98.22        perf-profile.children.cycles-pp.splice_direct_to_actor
     99.75            -1.4       98.36        perf-profile.children.cycles-pp.do_splice_direct
      2.39 ± 13%      -1.1        1.24 ± 16%  perf-profile.children.cycles-pp.alloc_pages
      2.63 ±  9%      -1.0        1.65 ±  8%  perf-profile.children.cycles-pp.__might_resched
      1.84 ± 12%      -0.8        1.02 ± 12%  perf-profile.children.cycles-pp.xas_load
      1.61 ± 12%      -0.8        0.84 ± 14%  perf-profile.children.cycles-pp.free_unref_page_commit
     99.79            -0.7       99.04        perf-profile.children.cycles-pp.do_sendfile
      4.18 ±  3%      -0.7        3.49 ± 13%  perf-profile.children.cycles-pp.generic_pipe_buf_release
      1.42 ± 11%      -0.6        0.80 ±  8%  perf-profile.children.cycles-pp.__cond_resched
      1.06 ± 11%      -0.5        0.59 ± 14%  perf-profile.children.cycles-pp.free_pcp_prepare
      0.94 ± 14%      -0.4        0.50 ± 15%  perf-profile.children.cycles-pp.__might_sleep
     99.80            -0.4       99.37        perf-profile.children.cycles-pp.__x64_sys_sendfile64
      0.75 ± 15%      -0.4        0.38 ± 16%  perf-profile.children.cycles-pp.policy_node
      0.79 ± 12%      -0.4        0.42 ± 15%  perf-profile.children.cycles-pp.__folio_put
      0.90 ± 10%      -0.4        0.54 ± 12%  perf-profile.children.cycles-pp._raw_spin_unlock_irqrestore
     99.95            -0.3       99.64        perf-profile.children.cycles-pp.do_syscall_64
     99.95            -0.3       99.68        perf-profile.children.cycles-pp.entry_SYSCALL_64_after_hwframe
      0.58 ± 12%      -0.3        0.31 ± 10%  perf-profile.children.cycles-pp.rcu_all_qs
      0.62 ± 14%      -0.3        0.36 ± 12%  perf-profile.children.cycles-pp.xas_start
      0.80 ± 10%      -0.2        0.56 ± 10%  perf-profile.children.cycles-pp.__list_del_entry_valid
      0.40 ± 17%      -0.2        0.20 ± 17%  perf-profile.children.cycles-pp._find_first_bit
      0.32 ± 14%      -0.2        0.16 ± 17%  perf-profile.children.cycles-pp.__list_add_valid
      0.34 ± 12%      -0.1        0.20 ±  8%  perf-profile.children.cycles-pp.sanity
      0.32 ± 11%      -0.1        0.18 ± 14%  perf-profile.children.cycles-pp.__page_cache_release
      0.27 ± 12%      -0.1        0.14 ± 15%  perf-profile.children.cycles-pp.should_fail_alloc_page
      0.25 ± 12%      -0.1        0.13 ± 17%  perf-profile.children.cycles-pp.__mem_cgroup_uncharge
      0.20 ± 14%      -0.1        0.10 ± 13%  perf-profile.children.cycles-pp.policy_nodemask
      0.12 ± 15%      -0.0        0.07 ± 12%  perf-profile.children.cycles-pp.pipe_to_null
      0.04 ± 45%      +0.0        0.07        perf-profile.children.cycles-pp.__libc_write
      0.05 ±  7%      +0.0        0.08 ± 11%  perf-profile.children.cycles-pp.ktime_get_coarse_real_ts64
      0.04 ± 71%      +0.0        0.07        perf-profile.children.cycles-pp.generic_file_write_iter
      0.04 ± 71%      +0.0        0.07 ±  5%  perf-profile.children.cycles-pp.generic_perform_write
      0.04 ± 71%      +0.0        0.07        perf-profile.children.cycles-pp.__generic_file_write_iter
      0.00            +0.1        0.05 ±  8%  perf-profile.children.cycles-pp.syscall_return_via_sysret
      0.00            +0.1        0.06 ± 11%  perf-profile.children.cycles-pp.ovl_d_real
      0.00            +0.1        0.07 ± 14%  perf-profile.children.cycles-pp.__put_user_nocheck_8
      0.16 ±  6%      +0.1        0.23 ±  2%  perf-profile.children.cycles-pp.current_time
      0.00            +0.1        0.08 ± 14%  perf-profile.children.cycles-pp.entry_SYSRETQ_unsafe_stack
      0.28 ±  8%      +0.1        0.37 ±  4%  perf-profile.children.cycles-pp.atime_needs_update
      0.09 ± 14%      +0.1        0.18 ± 15%  perf-profile.children.cycles-pp.__fsnotify_parent
      0.35 ±  9%      +0.1        0.45 ±  6%  perf-profile.children.cycles-pp.touch_atime
      0.00            +0.1        0.12 ± 12%  perf-profile.children.cycles-pp.__might_fault
      0.00            +0.1        0.14 ± 14%  perf-profile.children.cycles-pp._copy_from_user
      0.00            +0.1        0.14 ±  4%  perf-profile.children.cycles-pp.__entry_text_start
      0.00            +0.2        0.16 ± 19%  perf-profile.children.cycles-pp.__fdget
     83.76            +2.5       86.28 ±  2%  perf-profile.children.cycles-pp.generic_file_splice_read
     83.44            +2.5       85.99 ±  2%  perf-profile.children.cycles-pp.ovl_read_iter
     11.82 ± 13%      +6.4       18.26        perf-profile.children.cycles-pp.override_creds
     13.35 ± 14%      +7.7       21.06 ±  7%  perf-profile.children.cycles-pp.revert_creds
     10.81 ± 10%      -4.6        6.23 ±  9%  perf-profile.self.cycles-pp.memset_erms
      3.26 ± 13%      -1.5        1.74 ± 17%  perf-profile.self.cycles-pp.__alloc_pages
      3.02 ± 12%      -1.4        1.64 ± 14%  perf-profile.self.cycles-pp.free_unref_page
      2.96 ± 12%      -1.4        1.60 ± 14%  perf-profile.self.cycles-pp.rmqueue
      2.52 ± 13%      -1.2        1.30 ± 16%  perf-profile.self.cycles-pp.get_page_from_freelist
      2.58 ±  9%      -1.0        1.62 ±  8%  perf-profile.self.cycles-pp.__might_resched
      1.46 ± 13%      -0.7        0.78 ± 18%  perf-profile.self.cycles-pp.alloc_pages
      4.11 ±  3%      -0.7        3.44 ± 13%  perf-profile.self.cycles-pp.generic_pipe_buf_release
      1.40 ± 13%      -0.6        0.77 ± 15%  perf-profile.self.cycles-pp.__splice_from_pipe
      1.29 ± 12%      -0.6        0.68 ± 14%  perf-profile.self.cycles-pp.free_unref_page_commit
      1.37 ± 10%      -0.6        0.79 ±  9%  perf-profile.self.cycles-pp.append_pipe
      1.21 ± 12%      -0.5        0.67 ± 11%  perf-profile.self.cycles-pp.xas_load
      1.02 ± 12%      -0.5        0.54 ± 14%  perf-profile.self.cycles-pp.iov_iter_zero
      1.54 ±  8%      -0.5        1.08 ±  3%  perf-profile.self.cycles-pp.shmem_file_read_iter
      0.99 ± 11%      -0.4        0.55 ± 14%  perf-profile.self.cycles-pp.free_pcp_prepare
      0.80 ± 13%      -0.4        0.43 ± 15%  perf-profile.self.cycles-pp.__might_sleep
      0.82 ±  9%      -0.3        0.49 ±  5%  perf-profile.self.cycles-pp.__cond_resched
      0.78 ± 10%      -0.3        0.46 ± 12%  perf-profile.self.cycles-pp._raw_spin_unlock_irqrestore
      0.56 ± 13%      -0.2        0.32 ± 12%  perf-profile.self.cycles-pp.xas_start
      0.75 ± 10%      -0.2        0.54 ± 11%  perf-profile.self.cycles-pp.__list_del_entry_valid
      0.44 ± 13%      -0.2        0.23 ± 13%  perf-profile.self.cycles-pp.rcu_all_qs
      0.34 ± 16%      -0.2        0.17 ± 17%  perf-profile.self.cycles-pp._find_first_bit
      0.36 ± 15%      -0.2        0.18 ± 16%  perf-profile.self.cycles-pp.policy_node
      0.32 ± 12%      -0.2        0.17 ± 15%  perf-profile.self.cycles-pp.__page_cache_release
      0.34 ± 12%      -0.1        0.19 ±  8%  perf-profile.self.cycles-pp.sanity
      0.28 ± 14%      -0.1        0.14 ± 19%  perf-profile.self.cycles-pp.__list_add_valid
      0.24 ± 13%      -0.1        0.12 ± 15%  perf-profile.self.cycles-pp.__mem_cgroup_uncharge
      0.18 ± 14%      -0.1        0.10 ± 14%  perf-profile.self.cycles-pp.__folio_put
      0.16 ± 12%      -0.1        0.08 ± 12%  perf-profile.self.cycles-pp.policy_nodemask
      0.12 ±  9%      -0.1        0.06 ± 17%  perf-profile.self.cycles-pp.should_fail_alloc_page
      0.10 ± 13%      -0.0        0.06 ± 13%  perf-profile.self.cycles-pp.direct_splice_actor
      0.10 ± 14%      -0.0        0.06 ± 16%  perf-profile.self.cycles-pp.splice_from_pipe
      0.09 ± 14%      -0.0        0.06 ± 14%  perf-profile.self.cycles-pp.pipe_to_null
      0.10 ± 10%      +0.0        0.14 ±  6%  perf-profile.self.cycles-pp.current_time
      0.03 ± 70%      +0.0        0.08 ± 12%  perf-profile.self.cycles-pp.ktime_get_coarse_real_ts64
      0.00            +0.1        0.05 ±  8%  perf-profile.self.cycles-pp.syscall_return_via_sysret
      0.07 ± 15%      +0.1        0.13 ± 10%  perf-profile.self.cycles-pp.generic_file_splice_read
      0.00            +0.1        0.06 ± 11%  perf-profile.self.cycles-pp.ovl_d_real
      0.00            +0.1        0.07 ± 16%  perf-profile.self.cycles-pp.entry_SYSRETQ_unsafe_stack
      0.00            +0.1        0.07 ± 14%  perf-profile.self.cycles-pp.__put_user_nocheck_8
      0.09 ± 14%      +0.1        0.18 ± 15%  perf-profile.self.cycles-pp.__fsnotify_parent
      0.00            +0.1        0.14 ±  4%  perf-profile.self.cycles-pp.__entry_text_start
      0.00            +0.2        0.15 ± 20%  perf-profile.self.cycles-pp.__fdget
      0.11 ± 14%      +0.2        0.30 ± 14%  perf-profile.self.cycles-pp.splice_direct_to_actor
      0.00            +0.2        0.24 ± 11%  perf-profile.self.cycles-pp.do_sendfile
     11.40 ±  4%      +1.8       13.16 ±  3%  perf-profile.self.cycles-pp.__filemap_get_folio
     11.73 ± 13%      +6.4       18.12        perf-profile.self.cycles-pp.override_creds
     13.25 ± 14%      +7.6       20.88 ±  7%  perf-profile.self.cycles-pp.revert_creds



To reproduce:

        git clone https://github.com/intel/lkp-tests.git
        cd lkp-tests
        sudo bin/lkp install job.yaml           # job file is attached in this email
        bin/lkp split-job --compatible job.yaml # generate the yaml file for lkp run
        sudo bin/lkp run generated-yaml-file

        # if come across any failure that blocks the test,
        # please remove ~/.lkp and /lkp dir to run from a clean state.


Disclaimer:
Results have been estimated based on internal Intel analysis and are provided
for informational purposes only. Any difference in system hardware or software
design or configuration may affect actual performance.