09/11/2018 14:17, Thomas Monjalon: > 09/11/2018 11:03, Ferruh Yigit: > > On 11/8/2018 11:01 PM, Yongseok Koh wrote: > > > > > >> On Nov 8, 2018, at 9:21 AM, Ferruh Yigit <ferruh.yi...@intel.com> wrote: > > >> > > >> On 11/8/2018 3:59 PM, Thomas Monjalon wrote: > > >>> Hi, > > >>> > > >>> We need to gather more information about this bug. > > >>> More below. > > >>> > > >>> 07/11/2018 10:04, Wiles, Keith: > > >>>>> On Nov 6, 2018, at 9:30 PM, Yongseok Koh <ys...@mellanox.com> wrote: > > >>>>>> On Nov 5, 2018, at 6:06 AM, Wiles, Keith <keith.wi...@intel.com> > > >>>>>> wrote: > > >>>>>>> On Nov 2, 2018, at 9:04 PM, Yongseok Koh <ys...@mellanox.com> wrote: > > >>>>>>> > > >>>>>>> This is a workaround to prevent a crash, which might be caused by > > >>>>>>> optimization of newer gcc (7.3.0) on Intel Skylake. > > >>>>>> > > >>>>>> Should the code below not also test for the gcc version and > > >>>>>> the Sky Lake processor, maybe I am wrong but it seems it is > > >>>>>> turning AVX512 for all GCC builds > > >>>>> > > >>>>> I didn't want to check gcc version as 7.3.0 is very new. Only gcc 8 > > >>>>> is newly up since then (gcc 8.2). > > >>>>> Also, I wasn't able to test every gcc versions and I wanted to be a > > >>>>> bit conservative for this crash. > > >>>>> Performance drop (if any) by disabling a new (experimental) feature > > >>>>> would be less risky than unaccountable crash. > > >>>>> And, it does disable the feature only if CONFIG_RTE_ENABLE_AVX512=n. > > >>>>> Please refer to v3. > > >>>> > > >>>> Are you not turning off all of the GCC versions for AVX512. > > >>>> And you can test for range or greater then GCC version and > > >>>> it just seems like we are turning off every gcc version, is that true? > > >>> > > >>> Do we know exactly which GCC versions are affected? > > >>> > > >>>>>> Also bug 97 seems a bit obscure reference, maybe you know > > >>>>>> the bug report, but more details would be good? > > >>>>> > > >>>>> I sent out the report to dev list two month ago. > > >>>>> And I created the Bug 97 in order to reference it > > >>>>> in the commit message. > > >>>>> I didn't want to repeat same message here and there, > > >>>>> but it would've been better to have some sort of summary > > >>>>> of the Bug, although v3 has a few more words. > > >>>>> However, v3 has been merged. > > >>>> > > >>>> Still this is too obscure if nothing else give a link to > > >>>> a specific bug not just 97. > > >>> > > >>> The URL is > > >>> > > >>> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugs.dpdk.org%2Fshow_bug.cgi%3Fid%3D97&data=02%7C01%7Cyskoh%40mellanox.com%7C90ff6c361faf422b976108d6459eb490%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%7C0%7C636772945282345908&sdata=2o%2Fg203aWrKCYg16S6oI4BcS41igpLu1DloS%2FrRnknc%3D&reserved=0 > > >>> The bug is also pointing to an email: > > >>> > > >>> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmails.dpdk.org%2Farchives%2Fdev%2F2018-September%2F111522.html&data=02%7C01%7Cyskoh%40mellanox.com%7C90ff6c361faf422b976108d6459eb490%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%7C0%7C636772945282345908&sdata=NCFKxaREd69iZ8eyFKg%2FWBP73CLTXkxrNQQeii%2Bbsao%3D&reserved=0 > > >>> > > >>> Summary: > > >>> - CPU: Intel Skylake > > >>> - Linux environment: Ubuntu 18.04 > > >>> - Compiler: gcc-7.3 (Ubuntu 7.3.0-16ubuntu3) > > >> > > >> Is it possible to test a few other gcc versions to check if the issue is > > >> specific to this compiler version? > > > > > > Nothing's impossible but even with my quick search in gcc.gnu.org, > > > I could find the following documents mention mavx512f support: > > > > > > GCC 4.9.0 > > > April 22, 2014 (changes, documentation) > > > > > > GCC 5.1 > > > April 22, 2015 (changes, documentation) > > > > > > GCC 6.4 > > > July 4, 2017 (changes, documentation) > > > > > > GCC 7.1 > > > May 2, 2017 (changes, documentation) > > > > > > GCC 8.1 > > > May 2, 2018 (changes, documentation) > > > > > > We altogether have to put quite large resource to verify all of the > > > versions. > > > > > > I assumed older than gcc 7 would have the same issue. I know it was a > > > speculation > > > but like I mentioned I wanted to be more conservative. I didn't mean this > > > is a permanent fix. > > > For two months, we couldn't have any tangible solution (actually nobody > > > cared including myself), > > > so I submitted the patch to temporarily disable mavx512f. > > > > > > I'm still not sure what the best option is... > > > > For permanent fix we need more information, currently we can't re-produce > > this > > defect. Since you can reproduce it we need your support. > > > > Right now we don't know if this is compiler issue or code defect in > > rte_memcpy() > > or something else. > > > > It is easy to disable mavx512f as temporarily solution but it is coming > > with the > > cost of the performance drop, also without knowing the actual root cause I > > wouldn't say this is being conservative, actual issue may be just hidden > > with > > this change. > > > > I think as first thing we need to find a way to reproduce this issue in any > > other way than using mlx5 PMD. So that we can put more organized effort to > > fix this. > > I attached a simple unit test for rte_memcpy(), if this is a rte_memcpy() > > with > > avx512f defect as claimed, you should be able to see the issue with that, > > right? > > Did you able to find a chance to test it? Do you observer any crash there? > > I am able to connect to a machine where the issue is reproduced. > So I have tested replacing rte_memcpy with memcpy, > and the crash disappears when using memcpy. > So it confirms that the issue is in rte_memcpy.
One workaround is to disable CONFIG_RTE_ENABLE_AVX, but it is disabling AVX and AVX2 for all DPDK code. A more limited fix (tested) can be to disable AVX2 version of rte_memcpy and rely on the AVX version (which is not crashing): --- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h +++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h -#elif defined RTE_MACHINE_CPUFLAG_AVX2 +#elif defined RTE_MACHINE_CPUFLAG_AVX2_disable