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From: "Li, Xiaoyun" <xiaoyun.li@intel.com>
To: Thomas Monjalon <thomas@monjalon.net>, "Wang, Zhihong"
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CC: "dev@dpdk.org" <dev@dpdk.org>, "Richardson, Bruce"
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Thread-Topic: [dpdk-dev] [PATCH v8 1/3] eal/x86: run-time dispatch over memcpy
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Subject: Re: [dpdk-dev] [PATCH v8 1/3] eal/x86: run-time dispatch over memcpy
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> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> Sent: Thursday, November 2, 2017 18:45
> To: Wang, Zhihong <zhihong.wang@intel.com>; Li, Xiaoyun
> <xiaoyun.li@intel.com>
> Cc: dev@dpdk.org; Richardson, Bruce <bruce.richardson@intel.com>;
> Ananyev, Konstantin <konstantin.ananyev@intel.com>; Lu, Wenzhuo
> <wenzhuo.lu@intel.com>; Zhang, Helin <helin.zhang@intel.com>;
> ophirmu@mellanox.com
> Subject: Re: [dpdk-dev] [PATCH v8 1/3] eal/x86: run-time dispatch over
> memcpy
>=20
> 02/11/2017 11:22, Wang, Zhihong:
> > > I don't know what is creating this drop exactly.
> > > When doing different tests on different environments, we do not see
> > > this drop.
> > > If nobody else can see such issue, I guess we can ignore it.
> >
> > Hi Thomas, Xiaoyun,
> >
> > With this patch (commit 84cc318424d49372dd2a5fbf3cf84426bf95acce) I
> > see more than 20% performance drop in vhost loopback test with testpmd
> > macswap for 256 bytes packets, which means it impacts actual
> > vSwitching performance.
> >
> > Suggest we fix it or revert it for this release.
>=20
> I think we need more numbers to take a decision.
> What is the benefit of this patch? In which use-cases?

 The benefit is that if compile it on a lower platform (such as only suppor=
ts SSE),
when it run on higher platforms (such as AVX2 or AVX512). It would still ca=
n get ISA benefit (AVX2).
User case seems to be that some customers want it in cloud environment and =
don't want to compile on all platforms.

> What are the drawbacks? In which use-cases?

The drawback is perf drop. So far, see lot of drop in mellanox case and vho=
st case.

Should I send the revert patch or you revert it directly?

>=20
> Please, it is a call to test performance with and without this patch in m=
ore
> environments (CPU, packet size, applications).