Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization

[Bruce Richardson <bruce.richardson@intel.com>]

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@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@tuxdriver.com]
> >>>>>Sent: Monday, January 19, 2015 9:02 PM
> >>>>>To: Wang, Zhihong
> >>>>>Cc: dev@dpdk.org
> >>>>>Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
> >>>>>
> >>>>>On Mon, Jan 19, 2015 at 09:53:30AM +0800, zhihong.wang@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].

/Bruce