From: Rik van Riel <riel@redhat.com>
To: vatsa@linux.vnet.ibm.com
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Avi Kiviti <avi@redhat.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Mike Galbraith <efault@gmx.de>,
Chris Wright <chrisw@sous-sol.org>,
ttracy@redhat.com, dshaks@redhat.com
Subject: Re: [RFC -v5 PATCH 2/4] sched: Add yield_to(task, preempt) functionality.
Date: Fri, 14 Jan 2011 13:29:52 -0500 [thread overview]
Message-ID: <4D309620.60507@redhat.com> (raw)
In-Reply-To: <20110114174741.GB28632@linux.vnet.ibm.com>
On 01/14/2011 12:47 PM, Srivatsa Vaddagiri wrote:
> If I recall correctly, one of the motivations for yield_to_task (rather than
> a simple yield) was to avoid leaking bandwidth to other guests i.e we don't want
> the remaining timeslice of spinning vcpu to be given away to other guests but
> rather donate it to another (lock-holding) vcpu and thus retain the bandwidth
> allocated to the guest.
No, that was not the motivation. The motivation was to try
and get the lock holder to run soon, so it can release the
lock.
What you describe is merely one of the mechanisms considered
for meeting that objective.
> I am not sure whether we are meeting that objective via this patch, as
> lock-spinning vcpu would simply yield after setting next buddy to preferred
> vcpu on target pcpu, thereby leaking some amount of bandwidth on the pcpu
> where it is spinning.
Have you read the patch?
--
All rights reversed
next prev parent reply other threads:[~2011-01-14 18:29 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-14 8:02 [RFC -v5 PATCH 0/4] directed yield for Pause Loop Exiting Rik van Riel
2011-01-14 8:03 ` [RFC -v5 PATCH 1/4] kvm: keep track of which task is running a KVM vcpu Rik van Riel
2011-01-16 15:17 ` Avi Kivity
2011-01-14 8:03 ` [RFC -v5 PATCH 2/4] sched: Add yield_to(task, preempt) functionality Rik van Riel
2011-01-14 17:15 ` Peter Zijlstra
2011-01-14 17:47 ` Srivatsa Vaddagiri
2011-01-14 18:29 ` Rik van Riel [this message]
2011-01-17 15:53 ` Srivatsa Vaddagiri
2011-01-14 8:04 ` [RFC -v5 PATCH 3/4] export pid symbols needed for kvm_vcpu_on_spin Rik van Riel
2011-01-16 15:18 ` Avi Kivity
2011-01-14 8:05 ` [RFC -v5 PATCH 4/4] kvm: use yield_to instead of sleep in kvm_vcpu_on_spin Rik van Riel
2011-01-14 17:34 ` [RFC -v5 PATCH 0/4] directed yield for Pause Loop Exiting Rik van Riel
2011-01-14 21:29 ` Rik van Riel
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