Hi Neil, Any further comments on that one? Konstantin
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ananyev, Konstantin > Sent: Thursday, December 18, 2014 3:02 PM > To: Neil Horman > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH 10/17] librte_acl: add AVX2 as new > rte_acl_classify() method > > > > > -----Original Message----- > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > Sent: Wednesday, December 17, 2014 8:28 PM > > To: Ananyev, Konstantin > > Cc: dev at dpdk.org > > Subject: Re: [dpdk-dev] [PATCH 10/17] librte_acl: add AVX2 as new > > rte_acl_classify() method > > > > On Wed, Dec 17, 2014 at 07:22:06PM +0000, Ananyev, Konstantin wrote: > > > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > > > Sent: Wednesday, December 17, 2014 3:33 PM > > > > To: Ananyev, Konstantin > > > > Cc: dev at dpdk.org > > > > Subject: Re: [dpdk-dev] [PATCH 10/17] librte_acl: add AVX2 as new > > > > rte_acl_classify() method > > > > > > > > On Tue, Dec 16, 2014 at 04:16:48PM +0000, Ananyev, Konstantin wrote: > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > > > > > Sent: Monday, December 15, 2014 8:21 PM > > > > > > To: Ananyev, Konstantin > > > > > > Cc: dev at dpdk.org > > > > > > Subject: Re: [dpdk-dev] [PATCH 10/17] librte_acl: add AVX2 as new > > > > > > rte_acl_classify() method > > > > > > > > > > > > On Mon, Dec 15, 2014 at 04:33:47PM +0000, Ananyev, Konstantin wrote: > > > > > > > Hi Neil, > > > > > > > > > > > > > > > -----Original Message----- > > > > > > > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > > > > > > > Sent: Monday, December 15, 2014 4:00 PM > > > > > > > > To: Ananyev, Konstantin > > > > > > > > Cc: dev at dpdk.org > > > > > > > > Subject: Re: [dpdk-dev] [PATCH 10/17] librte_acl: add AVX2 as > > > > > > > > new rte_acl_classify() method > > > > > > > > > > > > > > > > On Sun, Dec 14, 2014 at 06:10:52PM +0000, Konstantin Ananyev > > > > > > > > wrote: > > > > > > > > > Introduce new classify() method that uses AVX2 instructions. > > > > > > > > > From my measurements: > > > > > > > > > On HSW boards when processing >= 16 packets per call, > > > > > > > > > AVX2 method outperforms it's SSE counterpart by 10-25%, > > > > > > > > > (depending on the ruleset). > > > > > > > > > At runtime, this method is selected as default one on HW that > > > > > > > > > supports AVX2. > > > > > > > > > > > > > > > > > > Signed-off-by: Konstantin Ananyev <konstantin.ananyev at > > > > > > > > > intel.com> > > > > > > > > > --- > > > > > > > > > lib/librte_acl/Makefile | 9 + > > > > > > > > > lib/librte_acl/acl.h | 4 + > > > > > > > > > lib/librte_acl/acl_run.h | 2 +- > > > > > > > > > lib/librte_acl/acl_run_avx2.c | 58 +++++ > > > > > > > > > lib/librte_acl/acl_run_avx2.h | 305 ++++++++++++++++++++++++ > > > > > > > > > lib/librte_acl/acl_run_sse.c | 537 > > > > > > > > > +----------------------------------------- > > > > > > > > > lib/librte_acl/acl_run_sse.h | 533 > > > > > > > > > +++++++++++++++++++++++++++++++++++++++++ > > > > > > > > > lib/librte_acl/rte_acl.c | 5 +- > > > > > > > > > lib/librte_acl/rte_acl.h | 2 + > > > > > > > > > 9 files changed, 917 insertions(+), 538 deletions(-) > > > > > > > > > create mode 100644 lib/librte_acl/acl_run_avx2.c > > > > > > > > > create mode 100644 lib/librte_acl/acl_run_avx2.h > > > > > > > > > create mode 100644 lib/librte_acl/acl_run_sse.h > > > > > > > > > > > > > > > > > > diff --git a/lib/librte_acl/Makefile b/lib/librte_acl/Makefile > > > > > > > > > index 65e566d..223ec31 100644 > > > > > > > > > --- a/lib/librte_acl/Makefile > > > > > > > > > +++ b/lib/librte_acl/Makefile > > > > > > > > > @@ -45,8 +45,17 @@ SRCS-$(CONFIG_RTE_LIBRTE_ACL) += acl_bld.c > > > > > > > > > SRCS-$(CONFIG_RTE_LIBRTE_ACL) += acl_gen.c > > > > > > > > > SRCS-$(CONFIG_RTE_LIBRTE_ACL) += acl_run_scalar.c > > > > > > > > > SRCS-$(CONFIG_RTE_LIBRTE_ACL) += acl_run_sse.c > > > > > > > > > +SRCS-$(CONFIG_RTE_LIBRTE_ACL) += acl_run_avx2.c > > > > > > > > > > > > > > > > > > CFLAGS_acl_run_sse.o += -msse4.1 > > > > > > > > > +ifeq ($(CC), icc) > > > > > > > > > +CFLAGS_acl_run_avx2.o += -march=core-avx2 > > > > > > > > > +else ifneq ($(shell \ > > > > > > > > > +test $(GCC_MAJOR_VERSION) -le 4 -a $(GCC_MINOR_VERSION) -le > > > > > > > > > 6 && echo 1), 1) > > > > > > > > > +CFLAGS_acl_run_avx2.o += -mavx2 > > > > > > > > > +else > > > > > > > > > +CFLAGS_acl_run_avx2.o += -msse4.1 > > > > > > > > > +endif > > > > > > > > > > > > > > > > > This seems broken. You've unilaterally included acl_run_avx2.c > > > > > > > > in the build > > > > > > > > list above, but only enable -mavx2 if the compiler is at least > > > > > > > > gcc 4.6. > > > > > > > > > > > > > > Actually 4.7 (before that version, as I know, gcc doesn't > > > > > > > support avx2) > > > > > > > > > > > > > > > Unless > > > > > > > > you want to make gcc 4.6 a requirement for building, > > > > > > > > > > > > > > I believe DPDK is required to be buildable by gcc 4.6 > > > > > > > As I remember, we have to support it all way down to gcc 4.3. > > > > > > > > > > > > > > > you need to also exclude > > > > > > > > the file above from the build list. > > > > > > > > > > > > > > That means that for gcc 4.6 and below rte_acl_classify_avx2() > > > > > > > would not be defined. > > > > > > > And then at runtime, I have to check for that somehow and > > > > > > > (re)populate classify_fns[]. > > > > > > > Doesn't seems like a good way to me. > > > > > > There are plenty of ways around that. > > > > > > > > > > > > At a minimum you could make the classify_fns array the one place > > > > > > that you need > > > > > > to add an ifdef __AVX__ call. > > > > > > > > > > > > You could also create a secondary definition of > > > > > > rte_acl_classify_avx2, and mark > > > > > > it as a weak symbol, which only returns -EOPNOTSUPP. That would be > > > > > > good, since > > > > > > the right thing will just automatically happen then if you don't > > > > > > build the > > > > > > actual avx2 classification code > > > > > > > > > > > > > Instead, I prefer to always build acl_run_avx2.c, > > > > > > > > > > > > > > > > But you can't do that. You just said above that you need to > > > > > > support down to gcc > > > > > > 4.3. I see you've worked around that with some additional ifdef > > > > > > __AVX__ > > > > > > instructions, but in so doing you ignore the possibiity that sse > > > > > > isn't > > > > > > supported, so you need to add __SSE__ checks now as well. > > > > > > ifdeffing that much > > > > > > just isn't scalable. > > > > > > > > > > We don't need to worry about compiler without SSE4.1 support. > > > > > I believe that all compilers that DDPDK has to build with, do support > > > > > SSE4.1. > > > > > So for SSE4.1 we only has to worry about situation when target CPU > > > > > doesn't support it > > > > > We manage it by runtime selection. > > > > > For AVX2 - situation is a bit different: it could be both compiler > > > > > and target CPU that don't support it. > > > > > > > > > > > And for your effort, you get an AVX2 classification path > > > > > > that potentially doesn't actually do vectorized classification. > > > > > > > > > > > > It really seems better to me to not build the code if the compiler > > > > > > doesn't > > > > > > support the instruction set it was meant to enable, and change the > > > > > > classification function pointer to something that informs the user > > > > > > of the lack > > > > > > of support at run time. > > > > > > > > > > > > > but for old compilers that don't support AVX2 - > > > > > > > rte_acl_classify_avx2() would simply be identical to > > > > > > > rte_acl_classify_sse(). > > > > > > > > > > > > > That doesn't make sense to me, for two reasons: > > > > > > > > > > > > 1) What if the machine being targeted doesn't support sse either? > > > > > > > > > > > > > > > > Exactly the same what is happening now on the machine with now SSE4.1 > > > > > support. > > > > > There is absolutely no difference here. > > > > > > > > > > > 2) If an application selects an AVX2 classifier, I as a developer > > > > > > expect to > > > > > > either get AVX2 based classification, or an error indicating that I > > > > > > can't do > > > > > > AVX2 classification, not a silent performance degradation down to > > > > > > scalar > > > > > > classification. > > > > > > > > > > In fact I was considering both variants for compilers not supporting > > > > > AVX2: > > > > > 1. silently degrade to SSE method. > > > > > 2. create a dummy function rte_acl_classify_error() and put it into > > > > > classify_fns[RTE_ACL_CLASSIFY_AVX2]. > > > > > > > > > > I choose #1 because it seems like a less distraction for the user - > > > > > all would keep working as before, user just wouldn't see any > > > > > improvement comparing to SSE method. > > > > > Again didn't want to spread "ifdef __AVX2__" into rte_acl.c > > > > > Though I don't have any strong opinion here. > > > > > So if you can provide some good reason why #2 is preferable, I am ok > > > > > to switch to #2. > > > > > > > > > Because 2 doesn't require any ifdeffing. As you note above the problem > > > > here is > > > > that AVX2 support is both compiler and machine dependent. If you make > > > > a weak > > > > symbol version of rte_acl_classify_avx2 that always gets built, then > > > > you've > > > > reduced the problem to just being compiler support, which you can check > > > > in the > > > > makefile. > > > > > > I don't think we'll get rid of ifdefing with #2. > > > We'll remove 2 ifdefs in acl_run_avx2.h, but then we have to introduce 2 > > > new in rte_acl.c instead. > > > From my understanding, we we'll need something like that: > > > > > > static const rte_acl_classify_t classify_fns[] = { > > > [RTE_ACL_CLASSIFY_DEFAULT] = rte_acl_classify_scalar, > > > [RTE_ACL_CLASSIFY_SCALAR] = rte_acl_classify_scalar, > > > [RTE_ACL_CLASSIFY_SSE] = rte_acl_classify_sse, > > > +#if (defined __GNUC__ && __GNUC__ <= 4 && __GNUC_MINOR__ < 7) > > > + [RTE_ACL_CLASSIFY_AVX2] = rte_acl_classify_error, > > > +#else > > > [RTE_ACL_CLASSIFY_AVX2] = rte_acl_classify_avx2, > > > +#endif > > > > > > You don't need to do this, you need to use a weak symbol: > > static int rte_acl_classify_avx2(...) __attributes__(weak) > > { > > return -EOPNOTSUP > > } > > > > > > Then in the rte_acl_avx2.c file define it again without the weak symbol > > > > That way, you do conditional compilation, and when you do the "real" symbol > > overrides the weak one. > > Ah yes, you right - not need for ifdef here, thought I still think we need > one below, in rte_acl_init(). > > > > > > }; > > > > > > static void __attribute__((constructor)) > > > rte_acl_init(void) > > > { > > > enum rte_acl_classify_alg alg = RTE_ACL_CLASSIFY_DEFAULT; > > > > > > +#if (defined __GNUC__ && __GNUC__ <= 4 && __GNUC_MINOR__ < 7) > > > if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_AVX2)) > > > alg = RTE_ACL_CLASSIFY_AVX2; > > > else if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE4_1)) > > > +#else > > > + if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE4_1)) > > > alg = RTE_ACL_CLASSIFY_SSE; > > > +#endif > > > rte_acl_set_default_classify(alg); > > > } > > > > > Why would you do this, this cpu feature flag definitions aren't matched to > > compiler support, it should always be defined. > > Because if we don't do this, then on machine that does support AVX2, > we'll always set CLASSIFY_AVX2 as default method, no matter was compiler > able to produce a proper code for it or not. > We should set CLASSIFY_AVX2 as default method only if both conditions are > met: > at build time compiler supports AVX2 and target cpu supports AVX2. > > Konstantin > > > You should still be able to > > check for AVX2 support in code that doesn't support emitting the > > instruction. > > > > Neil > > > > > Correct? > > > Konstantin > > > > > > > > > > > > > > > > > > > > > That in turn I think allows you to remove a > > > > > > > > bunch of the ifdeffing that you've done in some of the avx2 > > > > > > > > specific files. > > > > > > > > > > > > > > Actually there are not many of them. > > > > > > > One in acl_run_avx2.h and another in acl_run_avx2.c. > > > > > > > > > > > > > 2 in acl_run_avx2.h and 1 in rte_acl_osdep_alone.h, which is really > > > > > > 3 more than > > > > > > you need if you just do an intellegent weak classifier function > > > > > > defintion. > > > > > > > > > > grep -n __AVX2__ lib/librte_acl/*.[c,h] | grep -v endif > > > > > lib/librte_acl/acl_run_avx2.c:45:#ifdef __AVX2__ > > > > > lib/librte_acl/acl_run_avx2.h:36:#ifdef __AVX2__ > > > > > > > > > > rte_acl_osdep_alone.h - is a different story. > > > > > It needs to be there anyway, as in rte_common_vect.h. > > > > > In fact rte_acl_osdep_alone.h is only needed for cases when > > > > > RTE_LIBRTE_ACL_STANDALONE=y. > > > > > That comes from the old days, when we had to to support building > > > > > librte_acl library without the rest of DPDK. > > > > > I think we don't need it anymore and plan to remove it. > > > > > Just thought it should be in a separate patch. > > > > > Konstantin > > > > > > > > > > > > > > > > > Neil > > > > > > > >
