Re: [PATCH 0/4] DPDK memcpy optimization

[Marc Sune <marc.sune-kpkqNMk1I7M@public.gmane.org>]

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-VfR2kkLFssw@public.gmane.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-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org]
>>>>>>> Sent: Monday, January 19, 2015 9:02 PM
>>>>>>> To: Wang, Zhihong
>>>>>>> Cc: dev-VfR2kkLFssw@public.gmane.org
>>>>>>> Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
>>>>>>>
>>>>>>> On Mon, Jan 19, 2015 at 09:53:30AM +0800, zhihong.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org
>>>> 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

>
> /Bruce