From: Cyril Bur <cyrilbur@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Suraj Jitindar Singh <sjitindarsingh@gmail.com>, linuxppc-dev@ozlabs.org
Subject: Re: selftests/powerpc: Remove -flto from common CFLAGS
Date: Tue, 1 Mar 2016 10:08:25 +1100 [thread overview]
Message-ID: <20160301100825.67747147@camb691> (raw)
In-Reply-To: <20160229111013.71B58140779@ozlabs.org>
On Mon, 29 Feb 2016 22:10:13 +1100 (AEDT)
Michael Ellerman <mpe@ellerman.id.au> wrote:
> Hi Suraj,
>
> On Mon, 2016-29-02 at 06:29:55 UTC, Suraj Jitindar Singh wrote:
> > LTO can cause GCC to inline some functions which have attributes set. The
>
> You should define what LTO is the first time you use it.
>
> > act of inlining the functions can lead to GCC forgetting about the
> > attributes which leads to incorrect tests.
> > Notable example being: __attribute__((__target__("no-vsx")))
>
> That is probably a GCC bug, but we still need to work around it for now.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70010
>
> > LTO can also interact strangely with custom assembly functions and cause
> > tests to intermittently fail.
>
> That's probably Cyril writing bad asm :)
No doubt.
>
> > Both these cases are hard to detect and require manual inspection of
> > binaries which is unlikely to happen for all tests. Furthermore, LTO
> > optimisations are not necessary for selftests and correctness is paramount
> > and as such it is best to disable LTO.
> >
> > LTO can be enabled on a per test basis.
> >
> > A pseries_le_defconfig kernel on a POWER8 was used to determine that the
> > same subset of selftests pass and fail with and without -flto in the
> > common Makefile.
> >
> > These tests always fail:
> > selftests: per_event_excludes [FAIL]
> > selftests: event_attributes_test [FAIL]
> > selftests: ebb_vs_cpu_event_test [FAIL]
> > selftests: cpu_event_vs_ebb_test [FAIL]
> > selftests: cpu_event_pinned_vs_ebb_test [FAIL]
>
> They shouldn't :)
>
> Are you running as root? Bare metal or guest?
>
Interesting. I believe this was run baremetal as root. I'm going to test the
patch in qemu at root. Is there a list of expected failures in certain
situations?
> > selftests: ipc_unmuxed [FAIL]
>
> That one is expected.
>
> cheers
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
next prev parent reply other threads:[~2016-02-29 23:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-29 6:29 [PATCH] selftests/powerpc: Remove -flto from common CFLAGS Suraj Jitindar Singh
2016-02-29 11:10 ` Michael Ellerman
2016-02-29 23:08 ` Cyril Bur [this message]
2016-02-29 23:35 ` Michael Ellerman
2016-03-01 3:11 ` Cyril Bur
2016-03-01 4:46 ` Suraj Jitindar Singh
2016-03-03 10:58 ` Michael Ellerman
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