[v4,2/2] gro: optimise redundant parsing of packets

  Currently the IPv6 extension headers are parsed twice: first in
ipv6_gro_receive, and then again in ipv6_gro_complete.

By using the new ->transport_proto field, and also storing the size of the
network header, we can avoid parsing extension headers a second time in
ipv6_gro_complete (which saves multiple memory dereferences and conditional
checks inside ipv6_exthdrs_len for a varying amount of extension headers in
IPv6 packets).

The implementation had to handle both inner and outer layers in case of
encapsulation (as they can't use the same field). I've applied a similar
optimisation to Ethernet.

Performance tests for TCP stream over IPv6 with a varying amount of
extension headers demonstrate throughput improvement of ~0.7%.

Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
---
v3 -> v4:
	- Updated commit msg as Eric suggested.
	- No code changes.
---
 include/net/gro.h      |  9 +++++++++
 net/ethernet/eth.c     | 14 +++++++++++---
 net/ipv6/ip6_offload.c | 20 +++++++++++++++-----
 3 files changed, 35 insertions(+), 8 deletions(-)
  

On Mon, 2023-03-20 at 18:00 +0100, Richard Gobert wrote:
> Currently the IPv6 extension headers are parsed twice: first in
> ipv6_gro_receive, and then again in ipv6_gro_complete.
> 
> By using the new ->transport_proto field, and also storing the size of the
> network header, we can avoid parsing extension headers a second time in
> ipv6_gro_complete (which saves multiple memory dereferences and conditional
> checks inside ipv6_exthdrs_len for a varying amount of extension headers in
> IPv6 packets).
> 
> The implementation had to handle both inner and outer layers in case of
> encapsulation (as they can't use the same field). I've applied a similar
> optimisation to Ethernet.
> 
> Performance tests for TCP stream over IPv6 with a varying amount of
> extension headers demonstrate throughput improvement of ~0.7%.

I'm surprised that the improvement is measurable: for large aggregate
packets a single ipv6_exthdrs_len() call is avoided out of tens calls
for the individual pkts. Additionally such figure is comparable to
noise level in my tests.

This adds a couple of additional branches for the common (no extensions
header) case. 

while patch 1/2 could be useful, patch 2/2 overall looks not worthy to
me.

I suggest to re-post for inclusion only patch 1, unless others have
strong different opinions.

Cheers,

Paolo
  

On Wed, Mar 22, 2023 at 2:59 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Mon, 2023-03-20 at 18:00 +0100, Richard Gobert wrote:
> > Currently the IPv6 extension headers are parsed twice: first in
> > ipv6_gro_receive, and then again in ipv6_gro_complete.
> >
> > By using the new ->transport_proto field, and also storing the size of the
> > network header, we can avoid parsing extension headers a second time in
> > ipv6_gro_complete (which saves multiple memory dereferences and conditional
> > checks inside ipv6_exthdrs_len for a varying amount of extension headers in
> > IPv6 packets).
> >
> > The implementation had to handle both inner and outer layers in case of
> > encapsulation (as they can't use the same field). I've applied a similar
> > optimisation to Ethernet.
> >
> > Performance tests for TCP stream over IPv6 with a varying amount of
> > extension headers demonstrate throughput improvement of ~0.7%.
>
> I'm surprised that the improvement is measurable: for large aggregate
> packets a single ipv6_exthdrs_len() call is avoided out of tens calls
> for the individual pkts. Additionally such figure is comparable to
> noise level in my tests.
>
> This adds a couple of additional branches for the common (no extensions
> header) case.
>
> while patch 1/2 could be useful, patch 2/2 overall looks not worthy to
> me.
>
> I suggest to re-post for inclusion only patch 1, unless others have
> strong different opinions.
>

+2

I have the same feeling/opinion.

> Cheers,
>
> Paolo
>
  

> On Wed, Mar 22, 2023 at 2:59 AM Paolo Abeni <pabeni@redhat.com> wrote:
> >
> > On Mon, 2023-03-20 at 18:00 +0100, Richard Gobert wrote:
> > > Currently the IPv6 extension headers are parsed twice: first in
> > > ipv6_gro_receive, and then again in ipv6_gro_complete.
> > >
> > > By using the new ->transport_proto field, and also storing the size of the
> > > network header, we can avoid parsing extension headers a second time in
> > > ipv6_gro_complete (which saves multiple memory dereferences and conditional
> > > checks inside ipv6_exthdrs_len for a varying amount of extension headers in
> > > IPv6 packets).
> > >
> > > The implementation had to handle both inner and outer layers in case of
> > > encapsulation (as they can't use the same field). I've applied a similar
> > > optimisation to Ethernet.
> > >
> > > Performance tests for TCP stream over IPv6 with a varying amount of
> > > extension headers demonstrate throughput improvement of ~0.7%.
> >
> > I'm surprised that the improvement is measurable: for large aggregate
> > packets a single ipv6_exthdrs_len() call is avoided out of tens calls
> > for the individual pkts. Additionally such figure is comparable to
> > noise level in my tests.

It's not simple but I made an effort to make a quiet environment.
Correct configuration allows for this kind of measurements to be made
as the test is CPU bound and noise is a variance that can be reduced with 
enough samples.

Environment example: (100Gbit NIC (mlx5), physical machine, i9 12th
gen)

    # power-management and hyperthreading disabled in BIOS
    # sysctl preallocate net mem
    echo 0 > /sys/devices/system/cpu/cpufreq/boost # disable turboboost
    ethtool -A enp1s0f0np0 rx off tx off autoneg off # no PAUSE frames

    # Single core performance
    for x in /sys/devices/system/cpu/cpu[1-9]*/online; do echo 0 >"$x"; done

    ./network-testing-master/bin/netfilter_unload_modules.sh 2>/dev/null # unload netfilter
    tuned-adm profile latency-performance
    cpupower frequency-set -f 2200MHz # Set core to specific frequency
    systemctl isolate rescue-ssh.target
    # and kill all processes besides init

> > This adds a couple of additional branches for the common (no extensions
> > header) case.

The additional branch in ipv6_gro_receive would be negligible or even
non-existent for a branch predictor in the common case
(non-encapsulated packets).
I could wrap it with a likely macro if you wish.
Inside ipv6_gro_complete a couple of branches are saved for the common
case as demonstrated below.

original code ipv6_gro_complete (ipv6_exthdrs_len is inlined):

    // if (skb->encapsulation)

    ffffffff81c4962b:	f6 87 81 00 00 00 20 	testb  $0x20,0x81(%rdi)
    ffffffff81c49632:	74 2a                	je     ffffffff81c4965e <ipv6_gro_complete+0x3e>

    ...

    // nhoff += sizeof(*iph) + ipv6_exthdrs_len(iph, &ops);

    ffffffff81c4969c:	eb 1b                	jmp    ffffffff81c496b9 <ipv6_gro_complete+0x99>    <-- jump to beginning of for loop
    ffffffff81c4968e:   b8 28 00 00 00          mov    $0x28,%eax
    ffffffff81c49693:   31 f6                   xor    %esi,%esi
    ffffffff81c49695:   48 c7 c7 c0 28 aa 82    mov    $0xffffffff82aa28c0,%rdi
    ffffffff81c4969c:   eb 1b                   jmp    ffffffff81c496b9 <ipv6_gro_complete+0x99>
    ffffffff81c4969e:   f6 41 18 01             testb  $0x1,0x18(%rcx)
    ffffffff81c496a2:   74 34                   je     ffffffff81c496d8 <ipv6_gro_complete+0xb8>    <--- 3rd conditional check: !((*opps)->flags & INET6_PROTO_GSO_EXTHDR)
    ffffffff81c496a4:   48 98                   cltq  
    ffffffff81c496a6:   48 01 c2                add    %rax,%rdx
    ffffffff81c496a9:   0f b6 42 01             movzbl 0x1(%rdx),%eax
    ffffffff81c496ad:   0f b6 0a                movzbl (%rdx),%ecx
    ffffffff81c496b0:   8d 04 c5 08 00 00 00    lea    0x8(,%rax,8),%eax
    ffffffff81c496b7:   01 c6                   add    %eax,%esi
    ffffffff81c496b9:   85 c9                   test   %ecx,%ecx                                    <--- for loop starts here
    ffffffff81c496bb:   74 e7                   je     ffffffff81c496a4 <ipv6_gro_complete+0x84>    <--- 1st conditional check: proto != NEXTHDR_HOP
    ffffffff81c496bd:   48 8b 0c cf             mov    (%rdi,%rcx,8),%rcx
    ffffffff81c496c1:   48 85 c9                test   %rcx,%rcx
    ffffffff81c496c4:   75 d8                   jne    ffffffff81c4969e <ipv6_gro_complete+0x7e>    <--- 2nd conditional check: unlikely(!(*opps))
    
    ... (indirect call ops->callbacks.gro_complete)

ipv6_exthdrs_len contains a loop which has 3 conditional checks.
For the common (no extensions header) case, in the new code, *all 3
branches are completely avoided*

patched code ipv6_gro_complete:

    // if (skb->encapsulation)
    ffffffff81befe58:   f6 83 81 00 00 00 20    testb  $0x20,0x81(%rbx)
    ffffffff81befe5f:   74 78                   je     ffffffff81befed9 <ipv6_gro_complete+0xb9>
    
    ...
    
    // else
    ffffffff81befed9:	0f b6 43 50          	movzbl 0x50(%rbx),%eax
    ffffffff81befedd:	0f b7 73 4c          	movzwl 0x4c(%rbx),%esi
    ffffffff81befee1:	48 8b 0c c5 c0 3f a9 	mov    -0x7d56c040(,%rax,8),%rcx
    
    ... (indirect call ops->callbacks.gro_complete)

Thus, the patch is beneficial for both the common case and the ext hdr
case. I would appreciate a second consideration :)

> > while patch 1/2 could be useful, patch 2/2 overall looks not worthy to
> > me.
> >
> > I suggest to re-post for inclusion only patch 1, unless others have
> > strong different opinions.
> >
> 
> +2
> 
> I have the same feeling/opinion.
>
> > Cheers,
> >
> > Paolo
> >
  

On Wed, 2023-03-22 at 20:33 +0100, Richard Gobert wrote:
> > On Wed, Mar 22, 2023 at 2:59 AM Paolo Abeni <pabeni@redhat.com>
> > wrote:
> > > 
> > > On Mon, 2023-03-20 at 18:00 +0100, Richard Gobert wrote:
> > > > Currently the IPv6 extension headers are parsed twice: first in
> > > > ipv6_gro_receive, and then again in ipv6_gro_complete.
> > > > 
> > > > By using the new ->transport_proto field, and also storing the
> > > > size of the
> > > > network header, we can avoid parsing extension headers a second
> > > > time in
> > > > ipv6_gro_complete (which saves multiple memory dereferences and
> > > > conditional
> > > > checks inside ipv6_exthdrs_len for a varying amount of
> > > > extension headers in
> > > > IPv6 packets).
> > > > 
> > > > The implementation had to handle both inner and outer layers in
> > > > case of
> > > > encapsulation (as they can't use the same field). I've applied
> > > > a similar
> > > > optimisation to Ethernet.
> > > > 
> > > > Performance tests for TCP stream over IPv6 with a varying
> > > > amount of
> > > > extension headers demonstrate throughput improvement of ~0.7%.
> > > 
> > > I'm surprised that the improvement is measurable: for large
> > > aggregate
> > > packets a single ipv6_exthdrs_len() call is avoided out of tens
> > > calls
> > > for the individual pkts. Additionally such figure is comparable
> > > to
> > > noise level in my tests.
> 
> It's not simple but I made an effort to make a quiet environment.
> Correct configuration allows for this kind of measurements to be made
> as the test is CPU bound and noise is a variance that can be reduced
> with 
> enough samples.
> 
> Environment example: (100Gbit NIC (mlx5), physical machine, i9 12th
> gen)
> 
>     # power-management and hyperthreading disabled in BIOS
>     # sysctl preallocate net mem
>     echo 0 > /sys/devices/system/cpu/cpufreq/boost # disable
> turboboost
>     ethtool -A enp1s0f0np0 rx off tx off autoneg off # no PAUSE
> frames
> 
>     # Single core performance
>     for x in /sys/devices/system/cpu/cpu[1-9]*/online; do echo 0
> >"$x"; done
> 
>     ./network-testing-master/bin/netfilter_unload_modules.sh
> 2>/dev/null # unload netfilter
>     tuned-adm profile latency-performance
>     cpupower frequency-set -f 2200MHz # Set core to specific
> frequency
>     systemctl isolate rescue-ssh.target
>     # and kill all processes besides init
> 
> > > This adds a couple of additional branches for the common (no
> > > extensions
> > > header) case.
> 
> The additional branch in ipv6_gro_receive would be negligible or even
> non-existent for a branch predictor in the common case
> (non-encapsulated packets).
> I could wrap it with a likely macro if you wish.
> Inside ipv6_gro_complete a couple of branches are saved for the
> common
> case as demonstrated below.
> 
> original code ipv6_gro_complete (ipv6_exthdrs_len is inlined):
> 
>     // if (skb->encapsulation)
> 
>     ffffffff81c4962b:	f6 87 81 00 00 00 20 	testb 
> $0x20,0x81(%rdi)
>     ffffffff81c49632:	74 2a                	je    
> ffffffff81c4965e <ipv6_gro_complete+0x3e>
> 
>     ...
> 
>     // nhoff += sizeof(*iph) + ipv6_exthdrs_len(iph, &ops);
> 
>     ffffffff81c4969c:	eb 1b                	jmp   
> ffffffff81c496b9 <ipv6_gro_complete+0x99>    <-- jump to beginning of
> for loop
>     ffffffff81c4968e:   b8 28 00 00 00          mov    $0x28,%eax
>     ffffffff81c49693:   31 f6                   xor    %esi,%esi
>     ffffffff81c49695:   48 c7 c7 c0 28 aa 82    mov   
> $0xffffffff82aa28c0,%rdi
>     ffffffff81c4969c:   eb 1b                   jmp   
> ffffffff81c496b9 <ipv6_gro_complete+0x99>
>     ffffffff81c4969e:   f6 41 18 01             testb 
> $0x1,0x18(%rcx)
>     ffffffff81c496a2:   74 34                   je    
> ffffffff81c496d8 <ipv6_gro_complete+0xb8>    <--- 3rd conditional
> check: !((*opps)->flags & INET6_PROTO_GSO_EXTHDR)
>     ffffffff81c496a4:   48 98                   cltq  
>     ffffffff81c496a6:   48 01 c2                add    %rax,%rdx
>     ffffffff81c496a9:   0f b6 42 01             movzbl 0x1(%rdx),%eax
>     ffffffff81c496ad:   0f b6 0a                movzbl (%rdx),%ecx
>     ffffffff81c496b0:   8d 04 c5 08 00 00 00    lea   
> 0x8(,%rax,8),%eax
>     ffffffff81c496b7:   01 c6                   add    %eax,%esi
>     ffffffff81c496b9:   85 c9                   test   %ecx,%ecx    
> <--- for loop starts here
>     ffffffff81c496bb:   74 e7                   je    
> ffffffff81c496a4 <ipv6_gro_complete+0x84>    <--- 1st conditional
> check: proto != NEXTHDR_HOP
>     ffffffff81c496bd:   48 8b 0c cf             mov   
> (%rdi,%rcx,8),%rcx
>     ffffffff81c496c1:   48 85 c9                test   %rcx,%rcx
>     ffffffff81c496c4:   75 d8                   jne   
> ffffffff81c4969e <ipv6_gro_complete+0x7e>    <--- 2nd conditional
> check: unlikely(!(*opps))
>     
>     ... (indirect call ops->callbacks.gro_complete)
> 
> ipv6_exthdrs_len contains a loop which has 3 conditional checks.
> For the common (no extensions header) case, in the new code, *all 3
> branches are completely avoided*
> 
> patched code ipv6_gro_complete:
> 
>     // if (skb->encapsulation)
>     ffffffff81befe58:   f6 83 81 00 00 00 20    testb 
> $0x20,0x81(%rbx)
>     ffffffff81befe5f:   74 78                   je    
> ffffffff81befed9 <ipv6_gro_complete+0xb9>
>     
>     ...
>     
>     // else
>     ffffffff81befed9:	0f b6 43 50          	movzbl
> 0x50(%rbx),%eax
>     ffffffff81befedd:	0f b7 73 4c          	movzwl
> 0x4c(%rbx),%esi
>     ffffffff81befee1:	48 8b 0c c5 c0 3f a9 	mov    -
> 0x7d56c040(,%rax,8),%rcx
>     
>     ... (indirect call ops->callbacks.gro_complete)
> 
> Thus, the patch is beneficial for both the common case and the ext
> hdr
> case. I would appreciate a second consideration :)

A problem with the above analysis is that it does not take in
consideration the places where the new branch are added:
eth_gro_receive() and ipv6_gro_receive().

Note that such functions are called for each packet on the wire:
multiple times for each aggregate packets. 

The above is likely not measurable in terms on pps delta, but the added
CPU cycles spent for the common case are definitely there. In my
opinion that outlast the benefit for the extensions header case.

Cheers,

Paolo

p.s. please refrain from off-list ping. That is ignored by most and
considered rude by some.
  

> On Wed, 2023-03-22 at 20:33 +0100, Richard Gobert wrote:
> > > On Wed, Mar 22, 2023 at 2:59 AM Paolo Abeni <pabeni@redhat.com>
> > > wrote:
> > > > 
> > > > On Mon, 2023-03-20 at 18:00 +0100, Richard Gobert wrote:
> > > > > Currently the IPv6 extension headers are parsed twice: first in
> > > > > ipv6_gro_receive, and then again in ipv6_gro_complete.
> > > > > 
> > > > > By using the new ->transport_proto field, and also storing the
> > > > > size of the
> > > > > network header, we can avoid parsing extension headers a second
> > > > > time in
> > > > > ipv6_gro_complete (which saves multiple memory dereferences and
> > > > > conditional
> > > > > checks inside ipv6_exthdrs_len for a varying amount of
> > > > > extension headers in
> > > > > IPv6 packets).
> > > > > 
> > > > > The implementation had to handle both inner and outer layers in
> > > > > case of
> > > > > encapsulation (as they can't use the same field). I've applied
> > > > > a similar
> > > > > optimisation to Ethernet.
> > > > > 
> > > > > Performance tests for TCP stream over IPv6 with a varying
> > > > > amount of
> > > > > extension headers demonstrate throughput improvement of ~0.7%.
> > > > 
> > > > I'm surprised that the improvement is measurable: for large
> > > > aggregate
> > > > packets a single ipv6_exthdrs_len() call is avoided out of tens
> > > > calls
> > > > for the individual pkts. Additionally such figure is comparable
> > > > to
> > > > noise level in my tests.
> > 
> > It's not simple but I made an effort to make a quiet environment.
> > Correct configuration allows for this kind of measurements to be made
> > as the test is CPU bound and noise is a variance that can be reduced
> > with 
> > enough samples.
> > 
> > Environment example: (100Gbit NIC (mlx5), physical machine, i9 12th
> > gen)
> > 
> >     # power-management and hyperthreading disabled in BIOS
> >     # sysctl preallocate net mem
> >     echo 0 > /sys/devices/system/cpu/cpufreq/boost # disable
> > turboboost
> >     ethtool -A enp1s0f0np0 rx off tx off autoneg off # no PAUSE
> > frames
> > 
> >     # Single core performance
> >     for x in /sys/devices/system/cpu/cpu[1-9]*/online; do echo 0
> > >"$x"; done
> > 
> >     ./network-testing-master/bin/netfilter_unload_modules.sh
> > 2>/dev/null # unload netfilter
> >     tuned-adm profile latency-performance
> >     cpupower frequency-set -f 2200MHz # Set core to specific
> > frequency
> >     systemctl isolate rescue-ssh.target
> >     # and kill all processes besides init
> > 
> > > > This adds a couple of additional branches for the common (no
> > > > extensions
> > > > header) case.
> > 
> > The additional branch in ipv6_gro_receive would be negligible or even
> > non-existent for a branch predictor in the common case
> > (non-encapsulated packets).
> > I could wrap it with a likely macro if you wish.
> > Inside ipv6_gro_complete a couple of branches are saved for the
> > common
> > case as demonstrated below.
> > 
> > original code ipv6_gro_complete (ipv6_exthdrs_len is inlined):
> > 
> >     // if (skb->encapsulation)
> > 
> >     ffffffff81c4962b:	f6 87 81 00 00 00 20 	testb 
> > $0x20,0x81(%rdi)
> >     ffffffff81c49632:	74 2a                	je    
> > ffffffff81c4965e <ipv6_gro_complete+0x3e>
> > 
> >     ...
> > 
> >     // nhoff += sizeof(*iph) + ipv6_exthdrs_len(iph, &ops);
> > 
> >     ffffffff81c4969c:	eb 1b                	jmp   
> > ffffffff81c496b9 <ipv6_gro_complete+0x99>    <-- jump to beginning of
> > for loop
> >     ffffffff81c4968e:   b8 28 00 00 00          mov    $0x28,%eax
> >     ffffffff81c49693:   31 f6                   xor    %esi,%esi
> >     ffffffff81c49695:   48 c7 c7 c0 28 aa 82    mov   
> > $0xffffffff82aa28c0,%rdi
> >     ffffffff81c4969c:   eb 1b                   jmp   
> > ffffffff81c496b9 <ipv6_gro_complete+0x99>
> >     ffffffff81c4969e:   f6 41 18 01             testb 
> > $0x1,0x18(%rcx)
> >     ffffffff81c496a2:   74 34                   je    
> > ffffffff81c496d8 <ipv6_gro_complete+0xb8>    <--- 3rd conditional
> > check: !((*opps)->flags & INET6_PROTO_GSO_EXTHDR)
> >     ffffffff81c496a4:   48 98                   cltq  
> >     ffffffff81c496a6:   48 01 c2                add    %rax,%rdx
> >     ffffffff81c496a9:   0f b6 42 01             movzbl 0x1(%rdx),%eax
> >     ffffffff81c496ad:   0f b6 0a                movzbl (%rdx),%ecx
> >     ffffffff81c496b0:   8d 04 c5 08 00 00 00    lea   
> > 0x8(,%rax,8),%eax
> >     ffffffff81c496b7:   01 c6                   add    %eax,%esi
> >     ffffffff81c496b9:   85 c9                   test   %ecx,%ecx    
> > <--- for loop starts here
> >     ffffffff81c496bb:   74 e7                   je    
> > ffffffff81c496a4 <ipv6_gro_complete+0x84>    <--- 1st conditional
> > check: proto != NEXTHDR_HOP
> >     ffffffff81c496bd:   48 8b 0c cf             mov   
> > (%rdi,%rcx,8),%rcx
> >     ffffffff81c496c1:   48 85 c9                test   %rcx,%rcx
> >     ffffffff81c496c4:   75 d8                   jne   
> > ffffffff81c4969e <ipv6_gro_complete+0x7e>    <--- 2nd conditional
> > check: unlikely(!(*opps))
> >     
> >     ... (indirect call ops->callbacks.gro_complete)
> > 
> > ipv6_exthdrs_len contains a loop which has 3 conditional checks.
> > For the common (no extensions header) case, in the new code, *all 3
> > branches are completely avoided*
> > 
> > patched code ipv6_gro_complete:
> > 
> >     // if (skb->encapsulation)
> >     ffffffff81befe58:   f6 83 81 00 00 00 20    testb 
> > $0x20,0x81(%rbx)
> >     ffffffff81befe5f:   74 78                   je    
> > ffffffff81befed9 <ipv6_gro_complete+0xb9>
> >     
> >     ...
> >     
> >     // else
> >     ffffffff81befed9:	0f b6 43 50          	movzbl
> > 0x50(%rbx),%eax
> >     ffffffff81befedd:	0f b7 73 4c          	movzwl
> > 0x4c(%rbx),%esi
> >     ffffffff81befee1:	48 8b 0c c5 c0 3f a9 	mov    -
> > 0x7d56c040(,%rax,8),%rcx
> >     
> >     ... (indirect call ops->callbacks.gro_complete)
> > 
> > Thus, the patch is beneficial for both the common case and the ext
> > hdr
> > case. I would appreciate a second consideration :)
> 
> A problem with the above analysis is that it does not take in
> consideration the places where the new branch are added:
> eth_gro_receive() and ipv6_gro_receive().
> 
> Note that such functions are called for each packet on the wire:
> multiple times for each aggregate packets. 
> 
> The above is likely not measurable in terms on pps delta, but the added
> CPU cycles spent for the common case are definitely there. In my
> opinion that outlast the benefit for the extensions header case.
> 
> Cheers,
> 
> Paolo
> 
> p.s. please refrain from off-list ping. That is ignored by most and
> considered rude by some.

Thanks,
I will re-post the first patch as a new one.
As for the second patch, I get your point, you are correct. I didn't
pay enough attention to the accumulated overhead during the receive phase, as it
wasn't showing up in my measurements. I'll look further into it, and check if I
can come up with a better solution.

Sorry for the off-list ping, is it ok to send a ping via the mailing list?