linux-kernel - Re: [PATCH] kbuild: move -pipe to global KBUILD

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Message-ID: <20200222181249.GA23843@ubuntu-m2-xlarge-x86>
Date:   Sat, 22 Feb 2020 11:12:49 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
Cc:     Russell King <linux@...linux.org.uk>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, masahiroy@...nel.org,
        michal.lkml@...kovi.net
Subject: Re: [PATCH] kbuild: move -pipe to global KBUILD_CFLAGS

On Sat, Feb 22, 2020 at 09:24:14AM -0500, Alex Xu (Hello71) wrote:
> Excerpts from Nathan Chancellor's message of February 22, 2020 3:01 am:
> > I used hyperfine [1] to run a quick benchmark with a freshly built
> > GCC 9.2.0 for x86 and aarch64 and here are the results:
> > 
> > In both cases it seems like performance regresses (by 1% but still) but
> > maybe it is my machine, even though this benchmark was done on a
> > different machine than the one from my commit back in 2018.
> > 
> > I am not sure I would write off these results, since I did the benchmark
> > 25 times on each one back to back, eliminating most of the variance that
> > you described.
> > 
> > [1]: https://github.com/sharkdp/hyperfine
> > 
> > Cheers,
> > Nathan
> > 
> 
> What kernel version are you running? Do you have the 5.6 pipe reworks?

No, it is a stock Ubuntu 18.04 kernel, which is running 4.15.0.

$ uname -a
Linux c2-medium-x86 4.15.0-50-generic #54-Ubuntu SMP Mon May 6 18:46:08 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

If you are curious about the specs:

$ neofetch --stdout
nathan@...medium-x86 
-------------------- 
OS: Ubuntu 18.04.3 LTS x86_64 
Host: PowerEdge R6415 
Kernel: 4.15.0-50-generic 
Uptime: 126 days, 12 hours, 39 mins 
Packages: 686 
Shell: zsh 5.4.2 
Terminal: /dev/pts/0 
CPU: AMD EPYC 7401P 24- (48) @ 2.794GHz 
Memory: 2974MiB / 64018MiB 

Cheers,
Nathan