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Message-ID: <Z9axe9Ac5biyJjCC@gmail.com>
Date: Sun, 16 Mar 2025 12:09:47 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Herton Krzesinski <hkrzesin@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, hpa@...or.com,
linux-kernel@...r.kernel.org, olichtne@...hat.com,
atomasov@...hat.com, aokuliar@...hat.com
Subject: Re: [PATCH] x86: add back the alignment of the destination to 8
bytes in copy_user_generic()
* Ingo Molnar <mingo@...nel.org> wrote:
> > It does look good in my testing here, I built same kernel I was
> > using for testing the original patch (based on 6.14-rc6), this is
> > one of the results I got in one of the runs testing on the same
> > machine:
> >
> > CPU RATE SYS TIME sender-receiver
> > Server bind 19: 20.8Gbits/sec 14.832313000 20.863476111 75.4%-89.2%
> > Server bind 21: 18.0Gbits/sec 18.705221000 23.996913032 80.8%-89.7%
> > Server bind 23: 20.1Gbits/sec 15.331761000 21.536657212 75.0%-89.7%
> > Server bind none: 24.1Gbits/sec 14.164226000 18.043132731 82.3%-87.1%
> >
> > There are still some variations between runs, which is expected as
> > was the same when I tested my patch or in the not aligned case, but
> > it's consistently better/higher than the no align case. Looks
> > really it's sufficient to align for the higher than or equal 64
> > bytes copy case.
>
> Mind sending a v2 patch with a changelog and these benchmark numbers
> added in, and perhaps a Co-developed-by tag with Linus or so?
BTW., if you have a test system available, it would be nice to test a
server CPU in the Intel spectrum as well. (For completeness mostly, I'd
not expect there to be as much alignment sensitivity.)
The CPU you tested, AMD Epyc 7742 was launched ~6 years ago so it's
still within the window of microarchitectures we care about. An Intel
test would be nice from a similar timeframe as well. Older is probably
better in this case, but not too old. :-)
( Note that the Intel test is not required to apply the fix IMO - we
did change alignment patterns ~2 years ago in a5624566431d which
regressed. )
Thanks,
Ingo
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