From: David Woodhouse <dwmw2@infradead.org>
To: Alex Williamson <alex.williamson@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
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: Fri, 06 Nov 2020 17:18:08 +0000 [thread overview]
Message-ID: <F67D16D9-A5F0-4B40-8E1F-E713174D997B@infradead.org> (raw)
In-Reply-To: <20201106093200.6d8975ae@w520.home>
On 6 November 2020 16:32:00 GMT, Alex Williamson <alex.williamson@redhat.com> wrote:
>On Fri, 6 Nov 2020 11:17:21 +0100
>Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>> 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?
>> >
>>
>> Queued, except for patch 2/3 in the eventfd series which Alex hasn't
>> reviewed/acked yet.
>
>There was no vfio patch here, nor mention why it got dropped in v2
>afaict. Thanks,
That was a different (but related) series. The VFIO one is https://patchwork.kernel.org/project/kvm/patch/20201027135523.646811-3-dwmw2@infradead.org/
Thanks.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
next prev parent reply other threads:[~2020-11-06 17:18 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
2020-11-06 10:17 ` Paolo Bonzini
2020-11-06 16:32 ` Alex Williamson
2020-11-06 17:18 ` David Woodhouse [this message]
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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