From: Matthias Kaehlcke <email@example.com>
To: Nathan Chancellor <firstname.lastname@example.org>
Cc: Sasha Levin <email@example.com>,
Greg Kroah-Hartman <firstname.lastname@example.org>,
Nick Desaulniers <email@example.com>,
Subject: Re: Backport of commit a75bb4eb9e565b9f5115e2e8c07377ce32cbe69a
Date: Tue, 23 Apr 2019 12:56:28 -0700 [thread overview]
Message-ID: <20190423195628.GD112750@google.com> (raw)
On Tue, Apr 23, 2019 at 12:45:12PM -0700, Nathan Chancellor wrote:
> 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.
We picked it into our kernels because we needed a fix *now* to unbreak
our builds, but I agree it should be fixed at least in relevant LTS
> > 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
> > things?
> 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.
> : https://chromium.googlesource.com/chromiumos/third_party/kernel/+/8bb957d781e2350515c7cffd7e7dc0dfc1777f3b
> : https://source.codeaurora.org/quic/la/kernel/msm-4.9/commit/?id=e828e50380a34533c37eff98345847fd74667ddd
I suspect the Qualcomm tree would hit the VDSO issue if they use a
sufficiently recent version of clang.
Thanks Nathan for posting this to -stable, I should have cc-ed them in
the first place.
next prev parent reply other threads:[~2019-04-23 19:56 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
2019-04-23 19:56 ` Matthias Kaehlcke [this message]
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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