On Thu, 08 Nov 2018 16:59:22 +0100 Thomas Monjalon <tho...@monjalon.net> 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://bugs.dpdk.org/show_bug.cgi?id=97 > The bug is also pointing to an email: > https://mails.dpdk.org/archives/dev/2018-September/111522.html > > Summary: > - CPU: Intel Skylake > - Linux environment: Ubuntu 18.04 > - Compiler: gcc-7.3 (Ubuntu 7.3.0-16ubuntu3) > - Scenario: testpmd crashes when it starts forwarding > - Behaviour: AVX2 version of rte_memcpy() optimized with 512b > instructions > - Fix: disable AVX512 optimization with -mno-avx512f > > It seems to have been reproduced only when using mlx5 PMD so far. > Any other experience? > > I did a little checking, there are only a few machine types on Azure that are Skylake. These are obviously the high end lateset ones... https://azure.microsoft.com/en-us/blog/fv2-vms-are-now-available-the-fastest-vms-on-azure/
