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From: Paolo Bonzini <pbonzini@redhat.com>
To: David Woodhouse <dwmw2@infradead.org>,
	Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	kvm@vger.kernel.org
Subject: Re: [PATCH v2 1/2] sched/wait: Add add_wait_queue_priority()
Date: Wed, 4 Nov 2020 12:25:27 +0100	[thread overview]
Message-ID: <7fec9ad1-f5b9-6a02-64f7-95aa83668773@redhat.com> (raw)
In-Reply-To: <ef4660dba8135ca5a1dc7e854babcf65d8cef46f.camel@infradead.org>

On 04/11/20 10:35, David Woodhouse wrote:
> On Wed, 2020-10-28 at 15:35 +0100, Peter Zijlstra wrote:
>> On Tue, Oct 27, 2020 at 02:39:43PM +0000, David Woodhouse wrote:
>>> From: David Woodhouse <dwmw@amazon.co.uk>
>>>
>>> This allows an exclusive wait_queue_entry to be added at the head of the
>>> queue, instead of the tail as normal. Thus, it gets to consume events
>>> first without allowing non-exclusive waiters to be woken at all.
>>>
>>> The (first) intended use is for KVM IRQFD, which currently has
>>> inconsistent behaviour depending on whether posted interrupts are
>>> available or not. If they are, KVM will bypass the eventfd completely
>>> and deliver interrupts directly to the appropriate vCPU. If not, events
>>> are delivered through the eventfd and userspace will receive them when
>>> polling on the eventfd.
>>>
>>> By using add_wait_queue_priority(), KVM will be able to consistently
>>> consume events within the kernel without accidentally exposing them
>>> to userspace when they're supposed to be bypassed. This, in turn, means
>>> that userspace doesn't have to jump through hoops to avoid listening
>>> on the erroneously noisy eventfd and injecting duplicate interrupts.
>>>
>>> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
>>
>> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> 
> Thanks. Paolo, the conclusion was that you were going to take this set
> through the KVM tree, wasn't it?
> 

Yes.

Paolo


  reply	other threads:[~2020-11-04 11:25 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 17:53 [RFC PATCH 1/2] sched/wait: Add add_wait_queue_priority() David Woodhouse
2020-10-26 17:53 ` [RFC PATCH 2/2] kvm/eventfd: Use priority waitqueue to catch events before userspace David Woodhouse
2020-10-27  8:01   ` Paolo Bonzini
2020-10-27 10:15     ` David Woodhouse
2020-10-27 13:55     ` [PATCH 0/3] Allow in-kernel consumers to drain events from eventfd David Woodhouse
2020-10-27 13:55       ` [PATCH 1/3] eventfd: Export eventfd_ctx_do_read() David Woodhouse
2020-10-27 13:55       ` [PATCH 2/3] vfio/virqfd: Drain events from eventfd in virqfd_wakeup() David Woodhouse
2020-11-06 23:29         ` Alex Williamson
2020-11-08  9:17           ` Paolo Bonzini
2020-10-27 13:55       ` [PATCH 3/3] kvm/eventfd: Drain events from eventfd in irqfd_wakeup() David Woodhouse
2020-10-27 18:41         ` kernel test robot
2020-10-27 21:42         ` kernel test robot
2020-10-27 23:13         ` kernel test robot
2020-10-27 14:39 ` [PATCH v2 0/2] Allow KVM IRQFD to consistently intercept events David Woodhouse
2020-10-27 14:39   ` [PATCH v2 1/2] sched/wait: Add add_wait_queue_priority() David Woodhouse
2020-10-27 19:09     ` Peter Zijlstra
2020-10-27 19:27       ` David Woodhouse
2020-10-27 20:30         ` Peter Zijlstra
2020-10-27 20:49           ` David Woodhouse
2020-10-27 21:32           ` David Woodhouse
2020-10-28 14:20             ` Peter Zijlstra
2020-10-28 14:44               ` Paolo Bonzini
2020-10-28 14:35     ` Peter Zijlstra
2020-11-04  9:35       ` David Woodhouse
2020-11-04 11:25         ` Paolo Bonzini [this message]
2020-11-06 10:17         ` Paolo Bonzini
2020-11-06 16:32           ` Alex Williamson
2020-11-06 17:18             ` David Woodhouse
2020-10-27 14:39   ` [PATCH v2 2/2] kvm/eventfd: Use priority waitqueue to catch events before userspace David Woodhouse

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