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

[Marc Sune <marc.sune@bisdn.de>]

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

>