From: Gleb Natapov <gleb@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: mtosatti@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: emulator: do not needlesly sync registers from emulator ctxt to vcpu
Date: Wed, 30 Mar 2011 12:47:27 +0200 [thread overview]
Message-ID: <20110330104727.GS7766@redhat.com> (raw)
In-Reply-To: <4D93083D.6000806@redhat.com>
On Wed, Mar 30, 2011 at 12:38:53PM +0200, Avi Kivity wrote:
> On 03/29/2011 02:08 PM, Gleb Natapov wrote:
> >Currently we sync registers back and forth before/after exiting
> >to userspace for IO, but during IO device model shouldn't need to
> >read/write the registers, so we can as well skip those sync points. The
> >only exaception is broken vmware backdor interface. The new code sync
> >registers content during IO only if registers are read from/written to
> >by userspace in the middle of the IO operation and this almost never
> >happens in practise.
>
> While this is a nice idea, how much does it save in practice? It
> does introduce more complexity.
>
I haven't measured, but can try to do so. It eliminates two copies of
all registers on each MMIO/PIO read. I expect this to be measurable in
workloads that do many such reads.
--
Gleb.
next prev parent reply other threads:[~2011-03-30 10:47 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-29 12:08 [PATCH] KVM: emulator: do not needlesly sync registers from emulator ctxt to vcpu Gleb Natapov
2011-03-30 10:38 ` Avi Kivity
2011-03-30 10:47 ` Gleb Natapov [this message]
2011-03-30 10:50 ` Avi Kivity
2011-03-30 11:22 ` Gleb Natapov
2011-03-30 11:43 ` Gleb Natapov
2011-03-30 12:12 ` Avi Kivity
2011-03-30 12:12 ` Avi Kivity
2011-03-30 12:17 ` Avi Kivity
2011-03-30 12:48 ` Gleb Natapov
2011-03-30 13:26 ` Gleb Natapov
2011-03-30 13:29 ` Avi Kivity
2011-03-30 13:36 ` Gleb Natapov
2011-03-30 13:41 ` Avi Kivity
2011-03-30 13:43 ` Gleb Natapov
2011-03-30 13:46 ` Avi Kivity
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