linux-kernel - Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock

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Message-ID: <4D399CBD.10506@redhat.com>
Date:	Fri, 21 Jan 2011 09:48:29 -0500
From:	Rik van Riel <riel@...hat.com>
To:	vatsa@...ux.vnet.ibm.com
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Américo Wang 
	<xiyou.wangcong@...il.com>, Eric Dumazet <dada1@...mosbay.com>,
	Jan Beulich <JBeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	kvm@...r.kernel.org, suzuki@...ibm.com
Subject: Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock

On 01/21/2011 09:02 AM, Srivatsa Vaddagiri wrote:
> On Thu, Jan 20, 2011 at 09:56:27AM -0800, Jeremy Fitzhardinge wrote:
>>>   The key here is not to
>>> sleep when waiting for locks (as implemented by current patch-series, which can
>>> put other VMs at an advantage by giving them more time than they are entitled
>>> to)
>>
>> Why?  If a VCPU can't make progress because its waiting for some
>> resource, then why not schedule something else instead?
>
> In the process, "something else" can get more share of cpu resource than its
> entitled to and that's where I was bit concerned. I guess one could
> employ hard-limits to cap "something else's" bandwidth where it is of real
> concern (like clouds).

I'd like to think I fixed those things in my yield_task_fair +
yield_to + kvm_vcpu_on_spin patch series from yesterday.

https://lkml.org/lkml/2011/1/20/403

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