From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by dpdk.org (Postfix) with ESMTP id 4B21F5F44; Fri, 2 Nov 2018 22:46:13 +0100 (CET) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Nov 2018 14:46:12 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,457,1534834800"; d="scan'208";a="104848904" Received: from fyigit-mobl.ger.corp.intel.com (HELO [10.237.221.79]) ([10.237.221.79]) by fmsmga001.fm.intel.com with ESMTP; 02 Nov 2018 14:46:10 -0700 To: Yongseok Koh Cc: Thomas Monjalon , "bruce.richardson@intel.com" , "dev@dpdk.org" , Shahaf Shuler , "stable@dpdk.org" , Konstantin Ananyev , Anatoly Burakov References: <20181023212318.43082-1-yskoh@mellanox.com> <3a34ea82-fbdf-2ebd-c6d9-9713bfadefb8@intel.com> <20181102205926.GA15737@mtidpdk.mti.labs.mlnx> From: Ferruh Yigit Openpgp: preference=signencrypt Autocrypt: addr=ferruh.yigit@intel.com; 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WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181102205926.GA15737@mtidpdk.mti.labs.mlnx> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [dpdk-stable] [PATCH] build: disable compiler AVX512F support X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 02 Nov 2018 21:46:14 -0000 On 11/2/2018 8:59 PM, Yongseok Koh wrote: > On Fri, Nov 02, 2018 at 01:48:11PM +0000, Ferruh Yigit wrote: >> On 11/2/2018 12:42 PM, Ferruh Yigit wrote: >>> On 10/23/2018 10:23 PM, Yongseok Koh wrote: >>>> This is a workaround to prevent a crash, which might be caused by >>>> optimization of newer gcc (7.3.0) on Intel Skylake. >>>> >>>> Bugzilla ID: 97 >>> >>> After checking the defect description again, this is the issue observed in >>> rte_memcpy() implementation for AVX2, compiler uses AVX512F instructions while >>> compiling it which causes the failure, so this may be a compiler defect but we >>> don't know the root cause yet. >> >> Is the issue only with gcc, and only with specific version of gcc? >> If so can we reduce the disabling avx512 only to that gcc version? >> >>> >>> I think best solution is to find the root cause and fix either avx2 >>> implementation or compiler, but this seems won't be soon, at least for rc2. >>> >>> What this patch does is to prevent compiler to use avx512f instruction when >>> "CONFIG_RTE_ENABLE_AVX512=n". >>> >>> Concern is this will affect all DPDK generated code for x86, but since >>> rte_memcpy() in header file there is no way to disable using avx512f >>> instructions locally for rte_memcpy(). >>> I can't think of any other solution for now, so OK to go with this patch for >>> now. Please find below comment. >>> >>>> >>>> Cc: stable@dpdk.org >>>> >>>> Signed-off-by: Yongseok Koh >>>> --- >>>> config/x86/meson.build | 5 +++++ >>>> mk/rte.cpuflags.mk | 5 +++++ >>>> 2 files changed, 10 insertions(+) >>>> >>>> diff --git a/config/x86/meson.build b/config/x86/meson.build >>>> index 33efb5e547..e10ba872ac 100644 >>>> --- a/config/x86/meson.build >>>> +++ b/config/x86/meson.build >>>> @@ -47,6 +47,11 @@ endif >>>> if cc.get_define('__AVX512F__', args: march_opt) != '' >>>> dpdk_conf.set('RTE_MACHINE_CPUFLAG_AVX512F', 1) >>>> compile_time_cpuflags += ['RTE_CPUFLAG_AVX512F'] >>>> +else >>>> +# disable compiler's AVX512F support as a workaround for Bug 97 >>>> + if cc.has_argument('-mavx512f') >>>> + machine_args += '-mno-avx512f' >>>> + endif >>>> endif >>>> >>>> dpdk_conf.set('RTE_CACHE_LINE_SIZE', 64) >>>> diff --git a/mk/rte.cpuflags.mk b/mk/rte.cpuflags.mk >>>> index 43ed84155b..8fdb0cc2c3 100644 >>>> --- a/mk/rte.cpuflags.mk >>>> +++ b/mk/rte.cpuflags.mk >>>> @@ -68,6 +68,11 @@ endif >>>> ifneq ($(filter $(AUTO_CPUFLAGS),__AVX512F__),) >>>> ifeq ($(CONFIG_RTE_ENABLE_AVX512),y) >>>> CPUFLAGS += AVX512F >>>> +else >>>> +# disable compiler's AVX512F support as a workaround for Bug 97 >>>> +ifeq ($(shell $(CC) --target-help | grep -q mavx512f && echo 1), 1) >>> >>> This will not work for ICC, and do we need this? AUTO_CPUFLAGS already should >>> have what you are looking for, so I think this check can be removed. > > This is different from AUTO_CPUFLAGS as it tries to check compiler flag support. What AUTO_CPUFLAGS does? It is output of `cc -march=xxx -dM -E - < /dev/null`, which list defined macros for that specific march provided. Like if you use `-march=corei7` you won't see __AVX2__ set. And for `native`, if compiler doesn't support AVX2, I assume it won't able to output __AVX2__ Is there a case AUTO_CPUFLAGS has __AVX512F__ but "$(CC) --target-help" doesn't have `mavx512f`? > And per your question, I have only tested it with gcc, so I agree on applying it > only for gcc. Will submit v2. But, I don't think we need to check gcc version as > there's no fix reported yet in a newer gcc version and this patch would have > very limited impact. avx512f support is quite new and kinda experimental so > far. Dropping a bit of performance would be better than crash. :-) > > Thanks for your review, > Yongseok > >>>> +MACHINE_CFLAGS += -mno-avx512f >>>> +endif >>>> endif >>>> endif >>>> >>>> >>> >>