linux-kernel - Re: [PATCH] time,virt: resync steal time when guest & host lose sync

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Date:	Mon, 15 Aug 2016 11:00:44 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Radim Krcmar <rkrcmar@...hat.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH] time,virt: resync steal time when guest & host lose sync

On Mon, 2016-08-15 at 16:53 +0800, Wanpeng Li wrote:
> 2016-08-12 23:58 GMT+08:00 Rik van Riel <riel@...hat.com>:
> [...]
> > Wanpeng, does the patch below work for you?
> 
> It will break steal time for full dynticks guest, and there is a
> calltrace of thread_group_cputime_adjusted call stack, RIP is
> cputime_adjust+0xff/0x130.

How?  This patch is equivalent to passing ULONG_MAX to
steal_account_process_time, which you tried to no ill
effect before.

Do you have the full call trace?

> > Subject: time,virt: do not limit steal_account_process_time
> > 
> > When a guest is interrupted for a longer amount of time, missed
> > clock
> > ticks are not redelivered later. Because of that, we should not
> > limit
> 
> Interesting, so do we need to add a feature like lapic timer
> interrrupt coalescing in kvm? There is a RTC interrupt coalescing in
> qemu to handle the scenario you mentioned for windows guest, if we
> need a similar feature for linux guest? Paolo, Radim? I can try it if
> you think it's valuable. :)
> 
> Regards,
> Wanpeng Li
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