From: "Wang, Zhihong" <zhihong.wang@intel.com>
To: "EDMISON, Kelvin (Kelvin)" <kelvin.edmison@alcatel-lucent.com>,
"Stephen Hemminger" <stephen@networkplumber.org>,
Neil Horman <nhorman@tuxdriver.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
Date: Thu, 29 Jan 2015 01:53:32 +0000 [thread overview]
Message-ID: <F60F360A2500CD45ACDB1D700268892D0E773357@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <D0EE79A7.42BCB%kelvin.edmison@alcatel-lucent.com>
> -----Original Message-----
> From: EDMISON, Kelvin (Kelvin) [mailto:kelvin.edmison@alcatel-lucent.com]
> Sent: Thursday, January 29, 2015 5:48 AM
> To: Wang, Zhihong; Stephen Hemminger; Neil Horman
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
>
>
> On 2015-01-27, 3:22 AM, "Wang, Zhihong" <zhihong.wang@intel.com> wrote:
>
> >
> >
> >> -----Original Message-----
> >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of EDMISON,
> Kelvin
> >> (Kelvin)
> >> Sent: Friday, January 23, 2015 2:22 AM
> >> To: dev@dpdk.org
> >> Subject: Re: [dpdk-dev] [PATCH 0/4] DPDK memcpy optimization
> >>
> >>
> >>
> >> On 2015-01-21, 3:54 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:
> >> >>
> [..trim...]
> >> >> 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
> >>
> >> +1.
> >>
> >> I think it should be an anti-requirement that the build machine be
> >> the exact same chip as the deployment platform.
> >>
> >> I like the cpu flag inspection approach. It would help in the case
> >>where DPDK is in a VM and an odd set of CPU flags have been exposed.
> >>
> >> If that approach doesn't work though, then perhaps DPDK memcpy could
> >>go through a benchmarking at app startup time and select the most
> >>performant option out of a set, like mdraid's raid6 implementation
> >>does. To give an example, this is what my systems print out at boot
> >>time re: raid6 algorithm selection.
> >> raid6: sse2x1 3171 MB/s
> >> raid6: sse2x2 3925 MB/s
> >> raid6: sse2x4 4523 MB/s
> >> raid6: using algorithm sse2x4 (4523 MB/s)
> >>
> >> Regards,
> >> Kelvin
> >>
> >
> >Thanks for the proposal!
> >
> >For DPDK, performance is always the most important concern. We need to
> >utilize new architecture features to achieve that, so solution per arch
> >is necessary.
> >Even a few extra cycles can lead to bad performance if they're in a hot
> >loop.
> >For instance, let's assume DPDK takes 60 cycles to process a packet on
> >average, then 3 more cycles here means 5% performance drop.
> >
> >The dynamic solution is doable but with performance penalties, even if
> >it could be small. Also it may bring extra complexity, which can lead
> >to unpredictable behaviors and side effects.
> >For example, the dynamic solution won't have inline unrolling, which
> >can bring significant performance benefit for small copies with
> >constant length, like eth_addr.
> >
> >We can investigate the VM scenario more.
> >
> >Zhihong (John)
>
> John,
>
> Thanks for taking the time to answer my newbie question. I deeply
> appreciate the attention paid to performance in DPDK. I have a follow-up
> though.
>
> I'm trying to figure out what requirements this approach creates for the
> software build environment. If we want to build optimized versions for
> Haswell, Ivy Bridge, Sandy Bridge, etc, does this mean that we must have one
> of each micro-architecture available for running the builds, or is there a way
> of cross-compiling for all micro-architectures from just one build
> environment?
>
> Thanks,
> Kelvin
>
I'm not an expert in this, just some facts based on my test: The compile process depends on the compiler and the lib version.
So even on a machine that doesn't support the necessary ISA, it still should compile as long as gcc & glibc & etc have the support, only you'll get "Illegal instruction" trying launching the compiled binary.
Therefore if there's a way (worst case scenario: change flags manually) to make DPDK build process think that it's on a Haswell machine, it will produce Haswell binaries.
Zhihong (John)
next prev parent reply other threads:[~2015-01-29 1:53 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
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 [this message]
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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