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

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Jan 21, 2015 at 12:02:57PM +0000, Ananyev, Konstantin wrote:
> 
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Wang, Zhihong
> > Sent: Wednesday, January 21, 2015 3:44 AM
> > To: Richardson, Bruce; Neil Horman
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
> > 
> > 
> > 
> > > -----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.
> 
> We use instrincts and inlining in many other places too.
> Why it suddenly became a problem here?
I agree, something just doesnt feel right here.  not sure what it is yet, but I
don't see how a memcpy function can be so complex as to take almost 10 minutes
to compile.  Its almost like we're recursively including something here and its
driving gcc into a huge loop
Neil

> Konstantin
> 
> > 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)
> > 
> > 
> > 
> 
>