From: Peter Zijlstra <peterz@infradead.org>
To: Sean Christopherson <seanjc@google.com>, mhklinux@outlook.com
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Marc Zyngier <maz@kernel.org>,
Oliver Upton <oliver.upton@linux.dev>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
K Prateek Nayak <kprateek.nayak@amd.com>,
David Matlack <dmatlack@google.com>,
Juergen Gross <jgross@suse.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Subject: Re: [PATCH v2 08/12] sched/wait: Drop WQ_FLAG_EXCLUSIVE from add_wait_queue_priority()
Date: Wed, 21 May 2025 13:42:33 +0200 [thread overview]
Message-ID: <20250521114233.GC39944@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <aC0AEJX0FIMl9lDy@google.com>
On Tue, May 20, 2025 at 03:20:00PM -0700, Sean Christopherson wrote:
> On Tue, May 20, 2025, Peter Zijlstra wrote:
> > On Mon, May 19, 2025 at 11:55:10AM -0700, Sean Christopherson wrote:
> > > Drop the setting of WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() to
> > > differentiate it from add_wait_queue_priority_exclusive(). The one and
> > > only user add_wait_queue_priority(), Xen privcmd's irqfd_wakeup(),
> > > unconditionally returns '0', i.e. doesn't actually operate in exclusive
> > > mode.
> >
> > I find:
> >
> > drivers/hv/mshv_eventfd.c: add_wait_queue_priority(wqh, &irqfd->irqfd_wait);
> > drivers/xen/privcmd.c: add_wait_queue_priority(wqh, &kirqfd->wait);
> >
> > I mean, it might still be true and all, but hyperv seems to also use
> > this now.
>
> Oh FFS, another "heavily inspired by KVM". I should have bribed someone to take
> this series when I had the chance. *sigh*
>
> Unfortunately, the Hyper-V code does actually operate in exclusive mode. Unless
> you have a better idea, I'll tweak the series to:
>
> 1. Drop WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() and have the callers
> explicitly set the flag,
> 2. Add a patch to drop WQ_FLAG_EXCLUSIVE from Xen privcmd entirely.
> 3. Introduce add_wait_queue_priority_exclusive() and switch KVM to use it.
>
> That has an added bonus of introducing the Xen change in a dedicated patch, i.e.
> is probably a sequence anyways.
>
> Alternatively, I could rewrite the Hyper-V code a la the KVM changes, but I'm not
> feeling very charitable at the moment (the complete lack of documentation for
> their ioctl doesn't help).
Works for me. Michael is typically very responsive wrt hyperv (but you
probably know this).
next prev parent reply other threads:[~2025-05-21 11:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-05-19 18:55 [PATCH v2 00/12] KVM: Make irqfd registration globally unique Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 01/12] KVM: Use a local struct to do the initial vfs_poll() on an irqfd Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 02/12] KVM: Acquire SCRU lock outside of irqfds.lock during assignment Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 03/12] KVM: Initialize irqfd waitqueue callback when adding to the queue Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 04/12] KVM: Add irqfd to KVM's list via the vfs_poll() callback Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 05/12] KVM: Add irqfd to eventfd's waitqueue while holding irqfds.lock Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 06/12] sched/wait: Add a waitqueue helper for fully exclusive priority waiters Sean Christopherson
2025-05-20 19:17 ` Peter Zijlstra
2025-05-20 20:57 ` Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 07/12] KVM: Disallow binding multiple irqfds to an eventfd with a priority waiter Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 08/12] sched/wait: Drop WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() Sean Christopherson
2025-05-20 19:18 ` Peter Zijlstra
2025-05-20 22:20 ` Sean Christopherson
2025-05-21 11:42 ` Peter Zijlstra [this message]
2025-05-21 14:44 ` Michael Kelley
2025-05-21 15:05 ` Sean Christopherson
2025-05-21 13:22 ` Jürgen Groß
2025-05-19 18:55 ` [PATCH v2 09/12] KVM: Drop sanity check that per-VM list of irqfds is unique Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 10/12] KVM: selftests: Assert that eventfd() succeeds in Xen shinfo test Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 11/12] KVM: selftests: Add utilities to create eventfds and do KVM_IRQFD Sean Christopherson
2025-05-19 18:55 ` [PATCH v2 12/12] KVM: selftests: Add a KVM_IRQFD test to verify uniqueness requirements Sean Christopherson
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