From: Paolo Bonzini <pbonzini@redhat.com>
To: "Li, Liang Z" <liang.z.li@intel.com>,
"quintela@redhat.com" <quintela@redhat.com>
Cc: "amit.shah@redhat.com" <amit.shah@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"mst@redhat.com" <mst@redhat.com>
Subject: Re: [Qemu-devel] [v2 0/2] add avx2 instruction optimization
Date: Thu, 12 Nov 2015 09:43:45 +0100 [thread overview]
Message-ID: <56445141.2070907@redhat.com> (raw)
In-Reply-To: <F2CBF3009FA73547804AE4C663CAB28E019A44B6@shsmsx102.ccr.corp.intel.com>
On 12/11/2015 03:49, Li, Liang Z wrote:
> I am very surprised about the live migration performance result when
> I use your ' memeqzero4_paolo' instead of these SSE2 Intrinsics to
> check the zero pages.
What code were you using? Remember I suggested using only unsigned long
checks, like
unsigned long *p = ...
if (p[0] || p[1] || p[2] || p[3]
|| memcmp(p+4, p, size - 4 * sizeof(unsigned long)) != 0)
return BUFFER_NOT_ZERO;
else
return BUFFER_ZERO;
> The total live migration time increased about
> 8%! Not decreased. Although in the unit test your '
> memeqzero4_paolo' has better performance, any idea?
You only tested the case of zero pages. But real pages usually are not
zero, even if they have a few zero bytes at the beginning. It's very
important to optimize the initial check before the memcmp call.
Paolo
next prev parent reply other threads:[~2015-11-12 8:43 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-10 2:51 [Qemu-devel] [v2 0/2] add avx2 instruction optimization Liang Li
2015-11-10 2:51 ` [Qemu-devel] [v2 1/2] cutils: " Liang Li
2015-11-12 10:08 ` Paolo Bonzini
2015-11-12 10:12 ` Li, Liang Z
2015-11-12 11:30 ` Juan Quintela
2015-11-13 2:49 ` Li, Liang Z
2015-11-13 9:30 ` Paolo Bonzini
2015-11-12 14:43 ` Richard Henderson
2015-11-10 2:51 ` [Qemu-devel] [v2 2/2] configure: add options to config avx2 Liang Li
2015-11-10 3:43 ` [Qemu-devel] [v2 0/2] add avx2 instruction optimization Eric Blake
2015-11-10 5:48 ` Li, Liang Z
2015-11-10 9:13 ` Juan Quintela
2015-11-10 9:26 ` Li, Liang Z
2015-11-10 9:35 ` Paolo Bonzini
2015-11-10 9:41 ` Li, Liang Z
2015-11-10 9:50 ` Paolo Bonzini
2015-11-10 9:56 ` Li, Liang Z
2015-11-10 10:00 ` Paolo Bonzini
2015-11-10 10:04 ` Li, Liang Z
2015-11-12 2:49 ` Li, Liang Z
2015-11-12 8:43 ` Paolo Bonzini [this message]
2015-11-12 8:53 ` Li, Liang Z
2015-11-12 9:04 ` Paolo Bonzini
2015-11-12 9:40 ` Li, Liang Z
2015-11-12 9:45 ` Paolo Bonzini
2015-11-12 9:53 ` Li, Liang Z
2015-11-12 11:34 ` Juan Quintela
2015-11-12 11:42 ` Li, Liang Z
2015-11-12 19:56 ` Dr. David Alan Gilbert
2015-11-12 20:20 ` Eric Blake
2016-04-07 11:09 ` Dr. David Alan Gilbert
2016-04-07 12:54 ` Michael S. Tsirkin
2016-04-07 13:42 ` Dr. David Alan Gilbert
2016-04-07 13:54 ` Paolo Bonzini
2015-11-10 9:30 ` Paolo Bonzini
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