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From: Ingo Molnar <mingo@elte.hu>
To: Avi Kivity <avi@qumranet.com>
Cc: kvm-devel <kvm-devel@lists.sourceforge.net>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: kvm & dyntick
Date: Sun, 14 Jan 2007 09:39:54 +0100	[thread overview]
Message-ID: <20070114083954.GB2913@elte.hu> (raw)
In-Reply-To: <45A7BF9F.5090508@qumranet.com>


* Avi Kivity <avi@qumranet.com> wrote:

> >( 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. )
> >  
> 
> What's the problem with the TSC?  The only issue I'm aware of is that 
> the tsc might go backwards if the vcpu is migrated to another host cpu 
> (easily fixed).

this is not a problem of KVM - this is a problem of this laptop: its TSC 
stops when going idle. So the TSC is fundamentally unusable for reliable 
timekeeping - and qemu doesnt offer pmtimer emulation to fall back to, 
so the dyntick kernel refused to go high-res under KVM. Once i added the 
hyper clocksource to fall back to, it could utilize the PIT and the 
lapic for clock-events.

	Ingo

  reply	other threads:[~2007-01-14  8:44 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-11 16:08 Avi Kivity
2007-01-12  5:34 ` Rik van Riel
2007-01-12  6:20 ` Ingo Molnar
2007-01-12 10:19   ` Ingo Molnar
2007-01-12 17:04     ` Avi Kivity
2007-01-14  8:39       ` Ingo Molnar [this message]
2007-01-12 23:25     ` [kvm-devel] " Dor Laor
2007-01-12 23:39       ` Thomas Gleixner
2007-01-14  8:51       ` Ingo Molnar

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