On Wed, Apr 24, 2019 at 1:46 AM Sasha Levin sashal@kernel.org wrote:
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+iCaRYQW4...
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.
Dropped my private for-5.0/kbuild-cc-optimization Git branch. One less patch to carry with me...
Thanks.
- Sedat -