[PATCH] zlib: Fix big performance regression

[Tom Rini]

On Sun, Jun 30, 2024 at 10:47:06AM +0200, Christophe Leroy wrote:
> 
> 
> Le 27/06/2024 à 21:40, Tom Rini a écrit :
> > On Thu, Jun 27, 2024 at 01:34:55PM -0600, Tom Rini wrote:
> > > On Thu, Jun 27, 2024 at 10:25:21AM +0200, Christophe Leroy wrote:
> > > 
> > > > Commit 340fdf1303dc ("zlib: Port fix for CVE-2016-9841 to U-Boot")
> > > > brings a big performance regression in inflate_fast(), which leads
> > > > to watchdog timer reset on powerpc 8xx.
> > > > 
> > > > It looks like that commit does more than what it describe, it
> > > > especially removed an important optimisation that was doing copies
> > > > using halfwords instead of bytes. That unexpected change multiplied
> > > > by almost 4 the time spent in inflate_fast() and increased by 40%
> > > > the overall time needed to uncompress linux kernel image.
> > > > 
> > > > So partially revert that commit but keep post incrementation as it
> > > > is the initial purpose of said commit.
> > > > 
> > > > Fixes: 340fdf1303dc ("zlib: Port fix for CVE-2016-9841 to U-Boot")
> > > > Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
> > > > ---
> > > >   lib/zlib/inffast.c | 51 ++++++++++++++++++++++++++++++++++++----------
> > > >   1 file changed, 40 insertions(+), 11 deletions(-)
> > > 
> > > Both this, and my mostly revert lead to CI failures around compression
> > > tests:
> > > https://source.denx.de/u-boot/u-boot/-/jobs/859329
> > 
> > A full revert however, is fine.
> > 
> 
> Is it that ? :
> 
> FAILED
> test/py/tests/test_ut.py::test_ut[ut_compression_compression_test_gzip]
> 
> It seems like when the optimisation was added by commit cd514aeb996e ("zlib:
> Optimize decompression"), only the pre-increment implementation was
> available.
> 
> When POSTINC was added by commit e89516f031db ("zlib: split up to match
> original source tree"), I guess it was not verified because POSTINC is
> #undef by zlib.h.
> 
> With the following change I don't get the FAILED
> ut_compression_compression_test_gzip CI anymore
> (https://source.denx.de/u-boot/custodians/u-boot-mpc8xx/-/jobs/859937)
> 
> diff --git a/lib/zlib/inffast.c b/lib/zlib/inffast.c
> index c271d85ea1..5dc0574202 100644
> --- a/lib/zlib/inffast.c
> +++ b/lib/zlib/inffast.c
> @@ -257,7 +257,7 @@ void inflate_fast(z_streamp strm, unsigned start)
>                         sfrom = (unsigned short *)(from - OFF);
>                         loops = len >> 1;
>                         do
> -                           PUP(sout) = get_unaligned(++sfrom);
> +                           PUP(sout) = get_unaligned(sfrom++);
>                         while (--loops);
>                         out = (unsigned char *)sout + OFF;
>                         from = (unsigned char *)sfrom + OFF;

Ah, thanks! Testing again now.

-- 
Tom
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