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

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

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