LTO can cause GCC to inline some functions which have attributes set. The
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")))
LTO can also interact strangely with custom assembly functions and cause
tests to intermittently fail.
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]
selftests: ipc_unmuxed [FAIL]
And the remaining tests PASS.
Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
---
tools/testing/selftests/powerpc/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
From: Michael Ellerman <mpe@ellerman.id.au> Date: 2016-02-29 11:10:13
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.
LTO can also interact strangely with custom assembly functions and cause
tests to intermittently fail.
That's probably Cyril writing bad asm :)
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?
On Mon, 29 Feb 2016 22:10:13 +1100 (AEDT)
Michael Ellerman [off-list ref] wrote:
Hi Suraj,
On Mon, 2016-29-02 at 06:29:55 UTC, Suraj Jitindar Singh wrote:
quoted
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.
quoted
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.
LTO can also interact strangely with custom assembly functions and cause
tests to intermittently fail.
That's probably Cyril writing bad asm :)
No doubt.
quoted
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?
From: Michael Ellerman <mpe@ellerman.id.au> Date: 2016-02-29 23:35:14
On Tue, 2016-03-01 at 10:08 +1100, Cyril Bur wrote:
On Mon, 29 Feb 2016 22:10:13 +1100 (AEDT)
Michael Ellerman [off-list ref] wrote:
quoted
On Mon, 2016-29-02 at 06:29:55 UTC, Suraj Jitindar Singh wrote:
quoted
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?
Nope.
Most of those require the perf paranoid level to be set, see eg:
tools/testing/selftests/powerpc/pmu/ebb/cpu_event_vs_ebb_test.c: SKIP_IF(require_paranoia_below(1));
cheers
On Mon, 29 Feb 2016 22:10:13 +1100 (AEDT)
Michael Ellerman [off-list ref] wrote:
Hi Suraj,
On Mon, 2016-29-02 at 06:29:55 UTC, Suraj Jitindar Singh wrote:
quoted
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.
quoted
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.
quoted
LTO can also interact strangely with custom assembly functions and cause
tests to intermittently fail.
That's probably Cyril writing bad asm :)
quoted
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?
The answer here is that /proc/sys/kernel/perf_event_paranoid defaults to 1 but
0 is needed for these tests to not SKIP. The standard harness does not decern
between skips and fails, running each test in powerpc/ shows SKIP/FAIL.
I have run four kernels under QEMU/KVM on a fairly busy VM box and I have the
same result for all 4. All had /proc/sys/kernel/perf_event_paranoid set to 0
before running the tests. Each test was run by it's self not with the
run_kselftest.sh script which hides SKIPs.
pseries_defconfig (BE) qemu/KVM PATCHED
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
pseries_defconfig (BE) qemu/KVM unpatched
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
pseries_le_defconfig (LE) qemu/KVM PATCHED
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
pseries_le_defconfig (LE) qemu/KVM unpatched
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
There were no matches for grep SKIP *.out for any of the four.
This patch appears to not have affected any of the tests.
Reviewed-by: Cyril Bur <redacted>
On Mon, 29 Feb 2016 22:10:13 +1100 (AEDT)
Michael Ellerman [off-list ref] wrote:
quoted
Hi Suraj,
On Mon, 2016-29-02 at 06:29:55 UTC, Suraj Jitindar Singh wrote:
quoted
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.
quoted
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.
quoted
LTO can also interact strangely with custom assembly functions and cause
tests to intermittently fail.
That's probably Cyril writing bad asm :)
quoted
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?
The answer here is that /proc/sys/kernel/perf_event_paranoid defaults to 1 but
0 is needed for these tests to not SKIP. The standard harness does not decern
between skips and fails, running each test in powerpc/ shows SKIP/FAIL.
I have run four kernels under QEMU/KVM on a fairly busy VM box and I have the
same result for all 4. All had /proc/sys/kernel/perf_event_paranoid set to 0
before running the tests. Each test was run by it's self not with the
run_kselftest.sh script which hides SKIPs.
pseries_defconfig (BE) qemu/KVM PATCHED
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
pseries_defconfig (BE) qemu/KVM unpatched
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
pseries_le_defconfig (LE) qemu/KVM PATCHED
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
pseries_le_defconfig (LE) qemu/KVM unpatched
# grep FAIL *.out
cpu_event_pinned_vs_ebb_test.out:[FAIL] Test FAILED on line 87
ipc_unmuxed.out:[FAIL] Test FAILED on line 38
per_event_excludes.out:[FAIL] Test FAILED on line 95
There were no matches for grep SKIP *.out for any of the four.
This patch appears to not have affected any of the tests.
Reviewed-by: Cyril Bur <redacted>
The same tests were run with /proc/sys/kernel/perf_event_paranoid set to 0 on an bare metal power8 system with the same results.
pseries_le_defconfig (LE) PATCHED
# grep FAIL results_patched
[FAIL] Test FAILED on line 95
selftests: per_event_excludes [FAIL]
[FAIL] Test FAILED on line 87
selftests: cpu_event_pinned_vs_ebb_test [FAIL]
selftests: ipc_unmuxed [FAIL]
pseries_le_defconfig (LE) unpatched
# grep FAIL results_unpatched
[FAIL] Test FAILED on line 95
selftests: per_event_excludes [FAIL]
[FAIL] Test FAILED on line 87
selftests: cpu_event_pinned_vs_ebb_test [FAIL]
selftests: ipc_unmuxed [FAIL]
Thus there was no change in the test results between the patched and unpatched systems.
From: Michael Ellerman <mpe@ellerman.id.au> Date: 2016-03-03 10:58:54
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
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")))
LTO can also interact strangely with custom assembly functions and cause
tests to intermittently fail.