From: Matthias Kaehlcke <mka@chromium.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Sasha Levin <sashal@kernel.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 12:56:28 -0700 [thread overview]
Message-ID: <20190423195628.GD112750@google.com> (raw)
In-Reply-To: <20190423194512.GA31444@archlinux-i9>
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.
> > 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 [2] so it
> would be nice to have this to avoid any further issues down the road.
>
> [1]: https://chromium.googlesource.com/chromiumos/third_party/kernel/+/8bb957d781e2350515c7cffd7e7dc0dfc1777f3b
> [2]: 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190423195628.GD112750@google.com \
--to=mka@chromium.org \
--cc=clang-built-linux@googlegroups.com \
--cc=gregkh@linuxfoundation.org \
--cc=natechancellor@gmail.com \
--cc=ndesaulniers@google.com \
--cc=sashal@kernel.org \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.