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Groups > linux.kernel > #1202899
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq |
| Date | 2015-08-07 18:50 +0200 |
| Message-ID | <pUT0e-5e5-21@gated-at.bofh.it> (permalink) |
| References | (5 earlier) <oVdu9-5W5-1@gated-at.bofh.it> <oXRnt-2Nq-33@gated-at.bofh.it> <pUNxw-5E5-31@gated-at.bofh.it> <pUNQS-6fD-19@gated-at.bofh.it> <pUT0d-5e5-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, Aug 07, 2015 at 09:41:31AM -0700, Christoph Hellwig wrote: > On Fri, Aug 07, 2015 at 01:14:15PM +0200, Peter Zijlstra wrote: > > On that, we cannot convert completions to swait. Because swait wake_all > > must not happen from IRQ context, and complete_all() typically is used > > from just that. > > If swait queues aren't useable from IRQ context they will be fairly > useless. What's the problem with making them irq safe? Its just the swait_wake_all() that is not. The entire purpose of them was to have something that allows bounded execution (RT and all). Since you can have unbounded numbers of tasks waiting on a waitqueue (well, reality has bounds of course, like total memory available etc..) a wake_all() can end up being many many wake_process() calls. We've had this be a problem in RT. So the proposed swait_wake_all() requires being called from task context, such that it can drop the lock (and IRQ disable) after every wakeup, and thereby guarantee that higher priority things will not experience undue latencies. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Peter Zijlstra <peterz@infradead.org> - 2015-08-07 13:00 +0200
Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Peter Zijlstra <peterz@infradead.org> - 2015-08-07 13:20 +0200
Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Christoph Hellwig <hch@infradead.org> - 2015-08-07 18:50 +0200
Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Peter Zijlstra <peterz@infradead.org> - 2015-08-07 18:50 +0200
Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Christoph Hellwig <hch@infradead.org> - 2015-08-09 08:50 +0200
Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Thomas Gleixner <tglx@linutronix.de> - 2015-08-17 22:40 +0200
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