From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: Re: [PATCH v4 3/5] hash: add fallback to software CRC32 implementation Date: Tue, 18 Nov 2014 16:36:24 -0500 Message-ID: <20141118213624.GF32375@hmsreliant.think-freely.org> References: <1409724351-23786-1-git-send-email-e_zhumabekov@sts.kz> <20141118144138.GB32375@hmsreliant.think-freely.org> <546B607B.9030808@sts.kz> <20141118160005.GC32375@hmsreliant.think-freely.org> <546B7E2D.7050705@sts.kz> <20141118174619.GE32375@hmsreliant.think-freely.org> <20141118175226.GC5840@bricha3-MOBL3> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: "dev-VfR2kkLFssw@public.gmane.org" To: Bruce Richardson Return-path: Content-Disposition: inline In-Reply-To: <20141118175226.GC5840@bricha3-MOBL3> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces-VfR2kkLFssw@public.gmane.org Sender: "dev" On Tue, Nov 18, 2014 at 05:52:27PM +0000, Bruce Richardson wrote: > On Tue, Nov 18, 2014 at 12:46:19PM -0500, Neil Horman wrote: > > On Tue, Nov 18, 2014 at 11:13:17PM +0600, Yerden Zhumabekov wrote: > > >=20 > > > 18.11.2014 22:00, Neil Horman =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > > On Tue, Nov 18, 2014 at 09:06:35PM +0600, Yerden Zhumabekov wrote= : > > > >> 18.11.2014 20:41, Neil Horman =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > >>> On Tue, Nov 18, 2014 at 08:03:40PM +0600, Yerden Zhumabekov wro= te: > > > >>>> /** > > > >>>> * Use single crc32 instruction to perform a hash on a 4 byte= value. > > > >>>> + * Fall back to software crc32 implementation in case SSE4.2 = is > > > >>>> + * not supported > > > >>>> * > > > >>>> * @param data > > > >>>> * Data to perform hash on. > > > >>>> @@ -376,11 +413,18 @@ crc32c_2words(uint64_t data, uint32_t in= it_val) > > > >>>> static inline uint32_t > > > >>>> rte_hash_crc_4byte(uint32_t data, uint32_t init_val) > > > >>>> { > > > >>>> - return _mm_crc32_u32(init_val, data); > > > >>>> +#ifdef RTE_MACHINE_CPUFLAG_SSE4_2 > > > >>>> + if (likely(crc32_alg =3D=3D CRC32_SSE42)) > > > >>>> + return _mm_crc32_u32(init_val, data); > > > >>>> +#endif > > > >>> you don't really need these ifdefs here anymore given that you = have a > > > >>> constructor to do the algorithm selection. In fact you need to= remove them, in > > > >>> the event you build on a system that doesn't support SSE42, but= run on a system > > > >>> that does. > > > >> Originally, I thought so as well. I wrote the code without these= ifdefs, > > > >> but it didn't compile on my machine which doesn't support SSE4.2= . Error > > > >> was triggered by nmmintrin.h which has a check for respective GC= C > > > >> extension. So I think these ifdefs are indeed required. > > > >> > > > > You need to edit the makefile so that the compiler gets passed th= e option > > > > -msse42. That way it will know to emit sse42 instructions. It wi= ll also allow > > > > you to remove the ifdef from the include file > > >=20 > > > In this case, I guess there are two options: > > > 1) modify all makefiles which use librte_hash > > > 2) move all function bodies from rte_hash_crc.h to separate module, > > > leaving prototype definitions there only. > > >=20 > > > Everybody's up for the second option? :) > > >=20 > > Crud, you're right, I didn't think about the header inclusion issue. = Is it > > worth adding the jump to enable the dynamic hash selection? > > Neil >=20 > Maybe for cases where SSE4.2 is not currently available, i.e. for gener= ic builds. > For builds where we have hardware support confirmed at compile time, ju= st use > the function from the header file. > Does that make sense? >=20 I'm not certain of that, as I don't think anything can be 'confirmed' at = compile time. I.e. just because you have sse42 at compile time doesn't guarantee= you have it at run time with a DSO. If you have these as macros, you need to= enable sse42 whereever you include the file so that the intrinsic works properly= . an alternate option would be to not use the intrinsic, and craft some exp= licit __asm__ statement that executes the right sse42 instructions. That way t= he asm is directly emitted, without requiring the -msse42 flag at all, and it wi= ll just work in all the files that call it. Neil > /Bruce > >=20 > > > --=20 > > > Sincerely, > > >=20 > > > Yerden Zhumabekov > > > State Technical Service > > > Astana, KZ > > >=20 > > >=20 > > >=20 >=20