From: Jim Thompson <jim@netgate.com>
To: Neil Horman <nhorman@tuxdriver.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
Date: Wed, 21 Jan 2015 15:25:40 -0600 [thread overview]
Message-ID: <53D2253B-DE20-486E-ADF0-DA02AAB1EF35@netgate.com> (raw)
In-Reply-To: <20150121205404.GB32617@hmsreliant.think-freely.org>
I’m not as concerned with compile times given the potential performance boost.
A long time ago (mid-80s) I was at Convex, and wanted to do a vector bcopy(), because it would make the I/O system (mostly disk then (*)) go faster.
The architect explained to me that the vector registers were for applications, not the kernel (as well as re-explaining the expense of vector context
switches, should the kernel be using the vector unit(s) and some application also wanted to use them.
The same is true today of AVX/AVX2, SSE, and even the AES-NI instructions. Normally we don’t use these in kernel code (which is traditionally where
the networking stack has lived).
The differences with DPDK are that a) entire cores (including the AVX/SSE units and even AES-NI (FPU) are dedicated to DPDK, and b) DPDK is a library,
and the resulting networking applications are exactly that, applications. The "operating system” is now a control plane.
Jim
(* Back then it was commonly thought that TCP would never be able to fill a 10Gbps Ethernet.)
> On Jan 21, 2015, at 2:54 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>
> On Wed, Jan 21, 2015 at 11:49:47AM -0800, Stephen Hemminger wrote:
>> On Wed, 21 Jan 2015 13:26:20 +0000
>> Bruce Richardson <bruce.richardson@intel.com> wrote:
>>
>>> On Wed, Jan 21, 2015 at 02:21:25PM +0100, Marc Sune wrote:
>>>>
>>>> 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@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
>>>>>>
>>>>> 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
>>>
>>> I agree, if it provides the speedups then we need to have it in - and quite possibly
>>> on by default, even.
>>>
>>> /Bruce
>>
>> One issue I have is that as a vendor we need to ship on binary, not different distributions
>> for each Intel chip variant. There is some support for multi-chip version functions
>> but only in latest Gcc which isn't in Debian stable. And the multi-chip version
>> of functions is going to be more expensive than inlining. For some cases, I have
>> seen that the overhead of fancy instructions looks good but have nasty side effects
>> like CPU stall and/or increased power consumption which turns of turbo boost.
>>
>>
>> Distro's in general have the same problem with special case optimizations.
>>
> What we really need is to do something like borrow the alternatives mechanism
> from the kernel so that we can dynamically replace instructions at run time
> based on cpu flags. That way we could make the choice at run time, and wouldn't
> have to do alot of special case jumping about.
> Neil
>
next prev parent reply other threads:[~2015-01-21 21:25 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-19 1:53 zhihong.wang
2015-01-19 1:53 ` [dpdk-dev] [PATCH 1/4] app/test: Disabled VTA for memcpy test in app/test/Makefile zhihong.wang
2015-01-19 1:53 ` [dpdk-dev] [PATCH 2/4] app/test: Removed unnecessary test cases in test_memcpy.c zhihong.wang
2015-01-19 1:53 ` [dpdk-dev] [PATCH 3/4] app/test: Extended test coverage in test_memcpy_perf.c zhihong.wang
2015-01-19 1:53 ` [dpdk-dev] [PATCH 4/4] lib/librte_eal: Optimized memcpy in arch/x86/rte_memcpy.h for both SSE and AVX platforms zhihong.wang
2015-01-20 17:15 ` Stephen Hemminger
2015-01-20 19:16 ` Neil Horman
2015-01-21 3:18 ` Wang, Zhihong
2015-01-25 20:02 ` Jim Thompson
2015-01-26 14:43 ` Wodkowski, PawelX
2015-01-27 5:12 ` Wang, Zhihong
2015-01-19 13:02 ` [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization Neil Horman
2015-01-20 3:01 ` Wang, Zhihong
2015-01-20 15:11 ` Neil Horman
2015-01-20 16:14 ` Bruce Richardson
2015-01-21 3:44 ` Wang, Zhihong
2015-01-21 11:40 ` Bruce Richardson
2015-01-21 12:02 ` Ananyev, Konstantin
2015-01-21 12:38 ` Neil Horman
2015-01-23 3:26 ` Wang, Zhihong
2015-01-21 12:36 ` Marc Sune
2015-01-21 13:02 ` Bruce Richardson
2015-01-21 13:21 ` Marc Sune
2015-01-21 13:26 ` Bruce Richardson
2015-01-21 19:49 ` Stephen Hemminger
2015-01-21 20:54 ` Neil Horman
2015-01-21 21:25 ` Jim Thompson [this message]
2015-01-22 0:53 ` Stephen Hemminger
2015-01-22 9:06 ` Luke Gorrie
2015-01-22 13:29 ` Jay Rolette
2015-01-22 18:27 ` Luke Gorrie
2015-01-22 19:36 ` Jay Rolette
2015-01-22 18:21 ` EDMISON, Kelvin (Kelvin)
2015-01-27 8:22 ` Wang, Zhihong
2015-01-28 21:48 ` EDMISON, Kelvin (Kelvin)
2015-01-29 1:53 ` Wang, Zhihong
2015-01-23 6:52 ` Wang, Zhihong
2015-01-26 18:29 ` Ananyev, Konstantin
2015-01-27 1:42 ` Wang, Zhihong
2015-01-27 11:30 ` Ananyev, Konstantin
2015-01-27 12:19 ` Ananyev, Konstantin
2015-01-28 2:06 ` Wang, Zhihong
2015-01-25 14:50 ` Luke Gorrie
2015-01-26 1:30 ` Wang, Zhihong
2015-01-26 8:03 ` Luke Gorrie
2015-01-27 7:19 ` Wang, Zhihong
2015-01-27 13:57 ` [dpdk-dev] [snabb-devel] " Luke Gorrie
2015-01-29 3:42 ` [dpdk-dev] " Fu, JingguoX
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