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 >
