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Message-Id: <1207935700.7524.4.camel@twins> Date: Fri, 11 Apr 2008 19:41:40 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Dan Upton <upton.dan.linux@...il.com> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu> Subject: Re: CFS rq lock question On Fri, 2008-04-11 at 19:37 +0200, Peter Zijlstra wrote: > On Fri, 2008-04-11 at 13:21 -0400, Dan Upton wrote: > > I'm poking around with some scheduler stuff, and there's something I'm > > not clear on for the CFS runqueue locks. The comments before > > __load_balance_iterator(...) in sched_fair.c suggests things can be > > dequeued even though the runqueue lock is held. Can things also be > > added to the queue while the lock is held? (Also, either way, what's > > the rationale that dequeueing is a safe procedure when somebody else > > holds a lock?) > > /* > * Load-balancing iterator. Note: while the runqueue stays locked > * during the whole iteration, the current task might be > * dequeued so the iterator has to be dequeue-safe. Here we > * achieve that by always pre-iterating before returning > * the current task: > */ > > I don't think this comment is correct, but if it were, it would only > apply to rq->curr, not for any enqueue/dequeue. > D'oh, I'm silly.. the task can be dequeued because we move it to another cpu. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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