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From: Sasha Levin <sashal@kernel.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Matthias Kaehlcke <mka@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux@googlegroups.com
Subject: Re: Backport of commit a75bb4eb9e565b9f5115e2e8c07377ce32cbe69a
Date: Tue, 23 Apr 2019 19:46:08 -0400	[thread overview]
Message-ID: <20190423234608.GU17719@sasha-vm> (raw)
In-Reply-To: <20190423200355.GA17824@archlinux-i9>

On Tue, Apr 23, 2019 at 01:03:55PM -0700, Nathan Chancellor wrote:
>On Tue, Apr 23, 2019 at 12:56:28PM -0700, Matthias Kaehlcke wrote:
>> 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:
>> >
>> > https://lore.kernel.org/lkml/CAG5bF+S6OvBnsaR6UpMCqjDR9_hMo6qRMHGiW+iCaRYQW4C3YA@mail.gmail.com/
>> >
>> > The Chromium guys hit this [1] 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
>> versions.
>>
>
>Of course, I wasn't implying that was a bad thing :) it's further
>justification for this being a stable worthy patch as it fixes a real
>world issue and could fix more.

Okay, this makes more sense. The upstream commit message failed to
mention this.

I've queued it up.

--
Thanks,
Sasha

  reply	other threads:[~2019-04-23 23:46 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
2019-04-23 20:03       ` Nathan Chancellor
2019-04-23 23:46         ` Sasha Levin [this message]
2019-04-24  5:58           ` Sedat Dilek

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