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Date: Thu, 27 Oct 2011 12:17:15 +0200
From: Avi Kivity <avi@redhat.com>
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To: Raghavendra K T <raghukt@linux.vnet.ibm.com>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Greg Kroah-Hartman <gregkh@suse.de>, "H. Peter Anvin" <hpa@zytor.com>,
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        Virtualization <virtualization@lists.linux-foundation.org>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>, x86@kernel.org,
        KVM <kvm@vger.kernel.org>, Dave Jiang <dave.jiang@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
        Xen <xen-devel@lists.xensource.com>,
        Sedat Dilek <sedat.dilek@gmail.com>, Yinghai Lu <yinghai@kernel.org>,
        Marcelo Tosatti <mtosatti@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Rik van Riel <riel@redhat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Suzuki Poulose <suzuki@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>, Ryan Harper <ryanh@us.ibm.com>
Subject: Re: [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to support
 pv-ticketlock
References: <20111023190307.16364.35381.sendpatchset@oc5400248562.ibm.com> <20111023190558.16364.2136.sendpatchset@oc5400248562.ibm.com> <4EA53A7D.300@redhat.com> <20111024122734.GA10634@linux.vnet.ibm.com> <4EA56385.9040302@redhat.com> <20111024135032.GB10634@linux.vnet.ibm.com> <4EA6FEC2.1060209@linux.vnet.ibm.com> <4EA7E21B.8020805@redhat.com> <4EA85A9D.5060203@linux.vnet.ibm.com>
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On 10/26/2011 09:08 PM, Raghavendra K T wrote:
> On 10/26/2011 04:04 PM, Avi Kivity wrote:
>> On 10/25/2011 08:24 PM, Raghavendra K T wrote:
> CCing Ryan also
>>>
>>> So then do also you foresee the need for directed yield at some point,
>>> to address LHP? provided we have good improvements to prove.
>>
>> Doesn't this patchset completely eliminate lock holder preemption?
>>
> Basically I was curious whether we can do more better with your
> directed yield discussions in https://lkml.org/lkml/2010/8/2/106 .
>
> I felt we can get little more improvement with doing directed yield to
> lock-holder in case of LHP than sleeping. But I may be wrong.
>
> So wanted to get the feedback, on whether I am thinking in right
> direction.

i guess donating some time to the lock holder could help, but not by
much. The problem with non-pv spinlocks is that you can't just sleep,
since no one will wake you up, so you have to actively boost the lock
holder.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.