On Wed, 21 Jan 2015 13:26:20 +0000 Bruce Richardson <bruce.richardson at intel.com> wrote:
> On Wed, Jan 21, 2015 at 02:21:25PM +0100, Marc Sune wrote: > > > > On 21/01/15 14:02, Bruce Richardson wrote: > > >On Wed, Jan 21, 2015 at 01:36:41PM +0100, Marc Sune wrote: > > >>On 21/01/15 04:44, Wang, Zhihong wrote: > > >>>>-----Original Message----- > > >>>>From: Richardson, Bruce > > >>>>Sent: Wednesday, January 21, 2015 12:15 AM > > >>>>To: Neil Horman > > >>>>Cc: Wang, Zhihong; dev at dpdk.org > > >>>>Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization > > >>>> > > >>>>On Tue, Jan 20, 2015 at 10:11:18AM -0500, Neil Horman wrote: > > >>>>>On Tue, Jan 20, 2015 at 03:01:44AM +0000, Wang, Zhihong wrote: > > >>>>>>>-----Original Message----- > > >>>>>>>From: Neil Horman [mailto:nhorman at tuxdriver.com] > > >>>>>>>Sent: Monday, January 19, 2015 9:02 PM > > >>>>>>>To: Wang, Zhihong > > >>>>>>>Cc: dev at dpdk.org > > >>>>>>>Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization > > >>>>>>> > > >>>>>>>On Mon, Jan 19, 2015 at 09:53:30AM +0800, zhihong.wang at intel.com > > >>>>wrote: > > >>>>>>>>This patch set optimizes memcpy for DPDK for both SSE and AVX > > >>>>platforms. > > >>>>>>>>It also extends memcpy test coverage with unaligned cases and > > >>>>>>>>more test > > >>>>>>>points. > > >>>>>>>>Optimization techniques are summarized below: > > >>>>>>>> > > >>>>>>>>1. Utilize full cache bandwidth > > >>>>>>>> > > >>>>>>>>2. Enforce aligned stores > > >>>>>>>> > > >>>>>>>>3. Apply load address alignment based on architecture features > > >>>>>>>> > > >>>>>>>>4. Make load/store address available as early as possible > > >>>>>>>> > > >>>>>>>>5. General optimization techniques like inlining, branch > > >>>>>>>>reducing, prefetch pattern access > > >>>>>>>> > > >>>>>>>>Zhihong Wang (4): > > >>>>>>>> Disabled VTA for memcpy test in app/test/Makefile > > >>>>>>>> Removed unnecessary test cases in test_memcpy.c > > >>>>>>>> Extended test coverage in test_memcpy_perf.c > > >>>>>>>> Optimized memcpy in arch/x86/rte_memcpy.h for both SSE and AVX > > >>>>>>>> platforms > > >>>>>>>> > > >>>>>>>> app/test/Makefile | 6 + > > >>>>>>>> app/test/test_memcpy.c | 52 +- > > >>>>>>>> app/test/test_memcpy_perf.c | 238 +++++--- > > >>>>>>>> .../common/include/arch/x86/rte_memcpy.h | 664 > > >>>>>>>+++++++++++++++------ > > >>>>>>>> 4 files changed, 656 insertions(+), 304 deletions(-) > > >>>>>>>> > > >>>>>>>>-- > > >>>>>>>>1.9.3 > > >>>>>>>> > > >>>>>>>> > > >>>>>>>Are you able to compile this with gcc 4.9.2? The compilation of > > >>>>>>>test_memcpy_perf is taking forever for me. It appears hung. > > >>>>>>>Neil > > >>>>>>Neil, > > >>>>>> > > >>>>>>Thanks for reporting this! > > >>>>>>It should compile but will take quite some time if the CPU doesn't > > >>>>>>support > > >>>>AVX2, the reason is that: > > >>>>>>1. The SSE & AVX memcpy implementation is more complicated than > > >>>>AVX2 > > >>>>>>version thus the compiler takes more time to compile and optimize 2. > > >>>>>>The new test_memcpy_perf.c contains 126 constants memcpy calls for > > >>>>>>better test case coverage, that's quite a lot > > >>>>>> > > >>>>>>I've just tested this patch on an Ivy Bridge machine with GCC 4.9.2: > > >>>>>>1. The whole compile process takes 9'41" with the original > > >>>>>>test_memcpy_perf.c (63 + 63 = 126 constant memcpy calls) 2. It takes > > >>>>>>only 2'41" after I reduce the constant memcpy call number to 12 + 12 > > >>>>>>= 24 > > >>>>>> > > >>>>>>I'll reduce memcpy call in the next version of patch. > > >>>>>> > > >>>>>ok, thank you. I'm all for optimzation, but I think a compile that > > >>>>>takes almost > > >>>>>10 minutes for a single file is going to generate some raised eyebrows > > >>>>>when end users start tinkering with it > > >>>>> > > >>>>>Neil > > >>>>> > > >>>>>>Zhihong (John) > > >>>>>> > > >>>>Even two minutes is a very long time to compile, IMHO. The whole of DPDK > > >>>>doesn't take that long to compile right now, and that's with a couple > > >>>>of huge > > >>>>header files with routing tables in it. Any chance you could cut > > >>>>compile time > > >>>>down to a few seconds while still having reasonable tests? > > >>>>Also, when there is AVX2 present on the system, what is the compile time > > >>>>like for that code? > > >>>> > > >>>> /Bruce > > >>>Neil, Bruce, > > >>> > > >>>Some data first. > > >>> > > >>>Sandy Bridge without AVX2: > > >>>1. original w/ 10 constant memcpy: 2'25" > > >>>2. patch w/ 12 constant memcpy: 2'41" > > >>>3. patch w/ 63 constant memcpy: 9'41" > > >>> > > >>>Haswell with AVX2: > > >>>1. original w/ 10 constant memcpy: 1'57" > > >>>2. patch w/ 12 constant memcpy: 1'56" > > >>>3. patch w/ 63 constant memcpy: 3'16" > > >>> > > >>>Also, to address Bruce's question, we have to reduce test case to cut > > >>>down compile time. Because we use: > > >>>1. intrinsics instead of assembly for better flexibility and can utilize > > >>>more compiler optimization > > >>>2. complex function body for better performance > > >>>3. inlining > > >>>This increases compile time. > > >>>But I think it'd be okay to do that as long as we can select a fair set > > >>>of test points. > > >>> > > >>>It'd be great if you could give some suggestion, say, 12 points. > > >>> > > >>>Zhihong (John) > > >>> > > >>> > > >>While I agree in the general case these long compilation times is painful > > >>for the users, having a factor of 2-8x in memcpy operations is quite an > > >>improvement, specially in DPDK applications which need to deal > > >>(unfortunately) heavily on them -- e.g. IP fragmentation and reassembly. > > >> > > >>Why not having a fast compilation by default, and a tunable config flag to > > >>enable a highly optimized version of rte_memcpy (e.g. RTE_EAL_OPT_MEMCPY)? > > >> > > >>Marc > > >> > > >Out of interest, are these 2-8x improvements something you have benchmarked > > >in these app scenarios? [i.e. not just in micro-benchmarks]. > > > > How much that micro-speedup will end up affecting the performance of the > > entire application is something I cannot say, so I agree that we should > > probably have some additional benchmarks before deciding that pays off > > maintaining 2 versions of rte_memcpy. > > > > There are however a bunch of possible DPDK applications that could > > potentially benefit; IP fragmentation, tunneling and specialized DPI > > applications, among others, since they involve a reasonable amount of > > memcpys per pkt. My point was, *if* it proves that is enough beneficial, why > > not having it optionally? > > > > Marc > > I agree, if it provides the speedups then we need to have it in - and quite > possibly > on by default, even. > > /Bruce One issue I have is that as a vendor we need to ship on binary, not different distributions for each Intel chip variant. There is some support for multi-chip version functions but only in latest Gcc which isn't in Debian stable. And the multi-chip version of functions is going to be more expensive than inlining. For some cases, I have seen that the overhead of fancy instructions looks good but have nasty side effects like CPU stall and/or increased power consumption which turns of turbo boost. Distro's in general have the same problem with special case optimizations.
