From: Peter Zijlstra <peterz@infradead.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: "André Almeida" <andrealmeid@igalia.com>,
"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
"Paul E . McKenney" <paulmck@kernel.org>,
"Boqun Feng" <boqun.feng@gmail.com>,
"H . Peter Anvin" <hpa@zytor.com>, "Paul Turner" <pjt@google.com>,
linux-api@vger.kernel.org,
"Christian Brauner" <brauner@kernel.org>,
David.Laight@aculab.com, carlos@redhat.com,
"Peter Oskolkov" <posk@posk.io>,
"Alexander Mikhalitsyn" <alexander@mihalicyn.com>,
"Chris Kennelly" <ckennelly@google.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Darren Hart" <dvhart@infradead.org>,
"Davidlohr Bueso" <dave@stgolabs.net>,
libc-alpha@sourceware.org, "Steven Rostedt" <rostedt@goodmis.org>,
"Jonathan Corbet" <corbet@lwn.net>,
"Noah Goldstein" <goldstein.w.n@gmail.com>,
"Daniel Colascione" <dancol@google.com>,
longman@redhat.com, kernel-dev@igalia.com
Subject: Re: [RFC PATCH 0/1] Add FUTEX_SPIN operation
Date: Fri, 26 Apr 2024 12:14:38 +0200 [thread overview]
Message-ID: <20240426101438.GA39183@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <875xw44fxk.fsf@oldenburg.str.redhat.com>
On Fri, Apr 26, 2024 at 11:43:51AM +0200, Florian Weimer wrote:
> * André Almeida:
>
> > With FUTEX2_SPIN flag set during a futex_wait(), the futex value is
> > expected to be the PID of the lock owner. Then, the kernel gets the
> > task_struct of the corresponding PID, and checks if it's running. It
> > spins until the futex is awaken, the task is scheduled out or if a
> > timeout happens. If the lock owner is scheduled out at any time, then
> > the syscall follows the normal path of sleeping as usual.
>
> PID or TID?
TID, just like PI_LOCK I would presume.
> I think we'd like to have at least one, possibly more, bits for free
> use, so the kernel ID comparison should at least mask off the MSB,
> possibly more.
Yeah, it should be using FUTEX_TID_MASK -- just like PI_LOCK :-)
I suppose the question is if this thing should then also imply
FUTEX_WAITERS or not.
next prev parent reply other threads:[~2024-04-26 10:15 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-25 20:43 [RFC PATCH 0/1] Add FUTEX_SPIN operation André Almeida
2024-04-25 20:43 ` [RFC PATCH 1/1] futex: " André Almeida
2024-04-26 9:43 ` [RFC PATCH 0/1] " Florian Weimer
2024-04-26 10:14 ` Peter Zijlstra [this message]
2024-04-26 10:26 ` Christian Brauner
2024-05-01 23:44 ` André Almeida
2024-05-02 8:45 ` Christian Brauner
2024-05-02 9:51 ` Florian Weimer
2024-05-02 10:14 ` Christian Brauner
2024-05-02 10:39 ` Florian Weimer
2024-05-02 13:08 ` Christian Brauner
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