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

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

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@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].
> 
> 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