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From: Rik van Riel <riel@redhat.com>
To: "Christoffer Dall" <cdall@linaro.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	kvm@vger.kernel.org, Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: vtime accounting
Date: Fri, 24 Mar 2017 10:55:50 -0400	[thread overview]
Message-ID: <1490367350.28917.0.camel@redhat.com> (raw)
In-Reply-To: <20170314082601.GC1277@cbox>

On Tue, 2017-03-14 at 09:26 +0100, Christoffer Dall wrote:
> On Mon, Mar 13, 2017 at 06:28:16PM +0100, Radim Krčmář wrote:
> > 2017-03-08 02:57-0800, Christoffer Dall:
> > > Hi Paolo,
> > > 
> > > I'm looking at improving KVM/ARM a bit by calling
> > > guest_exit_irqoff
> > > before enabling interrupts when coming back from the guest.
> > > 
> > > Unfortunately, this appears to mess up my view of CPU usage using
> > > something like htop on the host, because it appears all time is
> > > spent
> > > inside the kernel.
> > > 
> > > From my analysis, I think this is because we never handle any
> > > interrupts
> > > before enabling interrupts, where the x86 code does its
> > > handle_external_intr, and the result on ARM is that we never
> > > increment
> > > jiffies before doing the vtime accounting.
> > 
> > (Hm, the counting might be broken on nohz_full then.)
> > 
> 
> Don't you still have a scheduler tick even with nohz_full and
> something
> that will eventually update jiffies then?
> 

With nohz_full, the housekeeping CPU will get a
timer interrupt every single jiffy, and the
jiffies variable will get updated HZ times a
second.

      parent reply	other threads:[~2017-03-24 14:55 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-08 10:57 vtime accounting Christoffer Dall
2017-03-09  8:16 ` Paolo Bonzini
2017-03-13 17:28 ` Radim Krčmář
2017-03-14  8:26   ` Christoffer Dall
2017-03-14  8:55     ` Marc Zyngier
2017-03-14 11:12       ` Christoffer Dall
2017-03-14 11:46         ` Marc Zyngier
2017-03-14 16:58     ` Radim Krčmář
2017-03-14 17:09       ` Paolo Bonzini
2017-03-14 18:41         ` Christoffer Dall
2017-03-14 19:32           ` Radim Krčmář
2017-03-14 20:01             ` Christoffer Dall
2017-03-14 21:52               ` Radim Krčmář
2017-03-15  8:09                 ` Paolo Bonzini
2017-03-15  8:05           ` Paolo Bonzini
2017-03-15  8:30             ` Christoffer Dall
2017-03-14 18:39       ` Christoffer Dall
2017-03-14 20:27         ` Radim Krčmář
2017-03-14 21:53           ` Radim Krčmář
2017-03-15  8:43           ` Christoffer Dall
2017-03-15 15:57             ` Radim Krčmář
2017-03-15 16:48               ` Christoffer Dall
2017-03-15 17:09                 ` Radim Krčmář
2017-03-24 15:04             ` Rik van Riel
2017-03-27 12:29               ` Wanpeng Li
2017-03-24 14:55     ` Rik van Riel [this message]

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