mbox series

[v2,0/3] entry: inline syscall enter/exit functions

Message ID 20231218074520.1998026-1-svens@linux.ibm.com
Headers
Series entry: inline syscall enter/exit functions |

Message

Sven Schnelle Dec. 18, 2023, 7:45 a.m. UTC 
  Hi List,

looking into the performance of syscall entry/exit after s390 switched
to generic entry showed that there's quite some overhead calling some
of the entry/exit work functions even when there's nothing to do.
This patchset moves the entry and exit function to entry-common.h, so
non inlined code gets only called when there is some work pending.

I wrote a small program that just issues invalid syscalls in a loop.
On an s390 machine, this results in the following numbers:

without this series:

$ ./syscall 1000000000
runtime: 94.886581s / per-syscall 9.488658e-08s

with this series:

$ ./syscall 1000000000
runtime: 84.732391s / per-syscall 8.473239e-08s

so the time required for one syscall dropped from 94.8ns to
84.7ns, which is a drop of about 11%.

Sven Schnelle (3):
  entry: move exit to usermode functions to header file
  entry: move enter_from_user_mode() to header file
  entry: move syscall_enter_from_user_mode() to header file

 include/linux/entry-common.h |  94 +++++++++++++++++++++++++++++--
 kernel/entry/common.c        | 106 ++++-------------------------------
 2 files changed, 100 insertions(+), 100 deletions(-)

Changes in v2:
- don't move of exit_to_user_mode_loop() to header file