linux-kernel - Re: kvm & dyntick

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Date:	Fri, 12 Jan 2007 11:19:31 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...ranet.com>
Cc:	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: kvm & dyntick


* Ingo Molnar <mingo@...e.hu> wrote:

> > dyntick-enabled guest:
> > - reduce the load on the host when the guest is idling
> >   (currently an idle guest consumes a few percent cpu)
> 
> yeah. KVM under -rt already works with dynticks enabled on both the 
> host and the guest. (but it's more optimal to use a dedicated 
> hypercall to set the next guest-interrupt)

using the dynticks code from the -rt kernel makes the overhead of an 
idle guest go down by a factor of 10-15:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 2556 mingo     15   0  598m 159m 157m R  1.5  8.0   0:26.20 qemu

( for this to work on my system i have added a 'hyper' clocksource 
  hypercall API for KVM guests to use - this is needed instead of the 
  running-to-slowly TSC. )

	Ingo
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