From: Nathan Chancellor <firstname.lastname@example.org>
To: Sasha Levin <email@example.com>
Cc: Greg Kroah-Hartman <firstname.lastname@example.org>,
Nick Desaulniers <email@example.com>,
Subject: Re: Backport of commit a75bb4eb9e565b9f5115e2e8c07377ce32cbe69a
Date: Tue, 23 Apr 2019 12:45:12 -0700 [thread overview]
Message-ID: <20190423194512.GA31444@archlinux-i9> (raw)
On Tue, Apr 23, 2019 at 03:35:12PM -0400, Sasha Levin wrote:
> On Tue, Apr 23, 2019 at 12:04:21PM -0700, Nathan Chancellor wrote:
> > Hi Greg and Sasha,
> > Please apply this commit to 4.4 through 5.0 (patches are threaded in
> > reply to this one), which will prevent Clang from emitting references
> > to compiler runtime functions and doing some performance-killing
> > optimization when using CONFIG_CC_OPTIMIZE_FOR_SIZE.
> > Please let me know if I did something wrong or if there are any
> > objections.
> This looks like a fix for a performance regression, which don't usually
> end up in stable unless they are severe enough.
Yes and no. The original reason for the revert was because of the
compiler runtime functions:
The Chromium guys hit this  and have applied the patch for their
kernels, I think it should be applied for everyone.
> This patch looks simple enough, and seeing peterz on it suggests to me
> that this was significant enough for someone to notice. Is this really
> the case, or is this just one of those %0.01 performance regression
I don't know of anyone else who has hit this but Qualcomm enabled
CONFIG_CC_OPTIMIZE_FOR_SIZE in their 4.9 kernels with clang  so it
would be nice to have this to avoid any further issues down the road.
Thanks for the quick reply!
next prev parent reply other threads:[~2019-04-23 19:45 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-23 19:04 Backport of commit a75bb4eb9e565b9f5115e2e8c07377ce32cbe69a Nathan Chancellor
2019-04-23 19:04 ` [PATCH 4.14] Revert "kbuild: use -Oz instead of -Os when using clang" Nathan Chancellor
2019-04-23 19:04 ` [PATCH 4.19] " Nathan Chancellor
2019-04-23 19:04 ` [PATCH 4.4] " Nathan Chancellor
2019-04-23 19:04 ` [PATCH 4.9] " Nathan Chancellor
2019-04-23 19:04 ` [PATCH 5.0] " Nathan Chancellor
2019-04-23 19:35 ` Backport of commit a75bb4eb9e565b9f5115e2e8c07377ce32cbe69a Sasha Levin
2019-04-23 19:42 ` Nick Desaulniers
2019-04-23 19:45 ` Nathan Chancellor [this message]
2019-04-23 19:56 ` Matthias Kaehlcke
2019-04-23 20:03 ` Nathan Chancellor
2019-04-23 23:46 ` Sasha Levin
2019-04-24 5:58 ` Sedat Dilek
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