linux-kernel - Re: [RFC PATCH 2/3] sched: add yield

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Message-ID: <20101203172954.GC11725@linux.vnet.ibm.com>
Date:	Fri, 3 Dec 2010 22:59:54 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Mike Galbraith <efault@....de>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Avi Kiviti <avi@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Anthony Liguori <aliguori@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 2/3] sched: add yield_to function

On Fri, Dec 03, 2010 at 12:09:01PM -0500, Rik van Riel wrote:
> I don't see how that is going to help get the lock
> released, when the VCPU holding the lock is on another
> CPU.

Even the directed yield() is not guaranteed to get the lock released, given its
shooting in the dark?

Anyway, the intention of yield() proposed was not to get lock released
immediately (which will happen eventually), but rather to avoid inefficiency
associated with (long) spinning and at the same time make sure we are not
leaking our bandwidth to other guests because of a naive yield ..

- vatsa


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