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From: Michael Roth <michael.roth@amd.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Sean Christopherson <seanjc@google.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"x86@kernel.org" <x86@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH v2] KVM: SVM: use vmsave/vmload for saving/restoring additional host state
Date: Wed, 16 Dec 2020 11:07:40 -0600	[thread overview]
Message-ID: <20201216170740.d73xomotx4c3oxql@amd.com> (raw)
In-Reply-To: <f22e2410-d4e3-f5fd-8e40-4225a83851c0@redhat.com>

On Wed, Dec 16, 2020 at 04:23:22PM +0100, Paolo Bonzini wrote:
> On 16/12/20 16:12, Michael Roth wrote:
> > It looks like it does save us ~20-30 cycles vs. vmload, but maybe not
> > enough to justify the added complexity. Additionally, since we still
> > need to call vmload when we exit to userspace, it ends up being a bit
> > slower for this particular workload at least. So for now I'll plan on
> > sticking to vmload'ing after vmexit and moving that to the asm code
> > if there are no objections.
> 
> Yeah, agreed.  BTW you can use "./x86/run x86/vmexit.flat" from
> kvm-unit-tests to check the numbers for a wide range of vmexit paths.

Wasn't aware of that, this looks really useful. Thanks!

> 
> Paolo
> 
> > current v2 patch, sample 1
> >    ioctl entry: 1204722748832
> >    pre-run:     1204722749408 ( +576)
> >    post-run:    1204722750784 (+1376)
> >    ioctl exit:  1204722751360 ( +576)
> >    total cycles:         2528
> > 
> > current v2 patch, sample 2
> >    ioctl entry: 1204722754784
> >    pre-vmrun:   1204722755360 ( +576)
> >    post-vmrun:  1204722756720 (+1360)
> >    ioctl exit:  1204722757312 ( +592)
> >    total cycles          2528
> > 
> > wrgsbase, sample 1
> >    ioctl entry: 1346624880336
> >    pre-vmrun:   1346624880912 ( +576)
> >    post-vmrun:  1346624882256 (+1344)
> >    ioctl exit:  1346624882912 ( +656)
> >    total cycles          2576
> > 
> > wrgsbase, sample 2
> >    ioctl entry: 1346624886272
> >    pre-vmrun:   1346624886832 ( +560)
> >    post-vmrun:  1346624888176 (+1344)
> >    ioctl exit:  1346624888816 ( +640)
> >    total cycles:         2544
> > 
> 

  reply	other threads:[~2020-12-16 17:08 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-14 17:41 [PATCH v2] KVM: SVM: use vmsave/vmload for saving/restoring additional host state Michael Roth
2020-12-14 19:38 ` Sean Christopherson
2020-12-14 20:08   ` Andy Lutomirski
2020-12-14 22:02   ` Michael Roth
2020-12-14 22:23     ` Sean Christopherson
2020-12-14 22:29     ` Andy Lutomirski
2020-12-15 10:15       ` Paolo Bonzini
2020-12-15 18:17       ` Michael Roth
2020-12-16 15:12         ` Michael Roth
2020-12-16 15:23           ` Paolo Bonzini
2020-12-16 17:07             ` Michael Roth [this message]
2020-12-15 18:55   ` Michael Roth
2020-12-16 23:48     ` Sean Christopherson
2020-12-17  8:29       ` Paolo Bonzini

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