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

["Wang, Zhihong" <zhihong.wang@intel.com>]

> -----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)