From: Paolo Bonzini <pbonzini@redhat.com>
To: "Zhang, Yang Z" <yang.z.zhang@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Hansen, Dave" <dave.hansen@intel.com>,
"Li, Liang Z" <liang.z.li@intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "gleb@kernel.org" <gleb@kernel.org>,
"mtosatti@redhat.com" <mtosatti@redhat.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"x86@kernel.org" <x86@kernel.org>,
"joro@8bytes.org" <joro@8bytes.org>,
"Hao, Xudong" <xudong.hao@intel.com>
Subject: Re: [v6] kvm/fpu: Enable fully eager restore kvm FPU
Date: Fri, 24 Apr 2015 09:44:29 +0200 [thread overview]
Message-ID: <5539F45D.6020400@redhat.com> (raw)
In-Reply-To: <A9667DDFB95DB7438FA9D7D576C3D87E0ACBB2B5@SHSMSX104.ccr.corp.intel.com>
On 24/04/2015 03:16, Zhang, Yang Z wrote:
>> This is interesting since previous measurements on KVM have had
>> the exact opposite results. I think we need to understand this a
>> lot more.
>
> What I can tell is that vmexit is heavy. So it is reasonable to see
> the improvement under some cases, especially kernel is using eager
> FPU now which means each schedule may trigger a vmexit.
On the other hand vmexit is lighter and lighter on newer processors; a
Sandy Bridge has less than half the vmexit cost of a Core 2 (IIRC 1000
vs. 2500 clock cycles approximately).
Also, measurement were done on Westmere but Sandy Bridge is the first
processor to have XSAVEOPT and thus use eager FPU.
Paolo
next prev parent reply other threads:[~2015-04-24 7:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-23 21:13 [v6] kvm/fpu: Enable fully eager restore kvm FPU Liang Li
2015-04-23 10:40 ` Paolo Bonzini
2015-04-23 11:25 ` Jan Kiszka
2015-04-23 15:28 ` Dave Hansen
2015-04-23 20:28 ` H. Peter Anvin
2015-04-24 1:16 ` Zhang, Yang Z
2015-04-24 7:44 ` Paolo Bonzini [this message]
2015-04-24 7:46 ` Zhang, Yang Z
2015-04-24 7:55 ` Paolo Bonzini
2015-04-24 8:08 ` Zhang, Yang Z
2015-04-23 22:57 ` Wanpeng Li
2015-04-24 2:21 ` Rik van Riel
2015-04-23 23:17 ` Wanpeng Li
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