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From: Florian Weimer <fweimer@redhat.com>
To: "André Almeida" <andrealmeid@igalia.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	 Peter Zijlstra <peterz@infradead.org>,
	 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 11:43:51 +0200	[thread overview]
Message-ID: <875xw44fxk.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20240425204332.221162-1-andrealmeid@igalia.com> ("André Almeida"'s message of "Thu, 25 Apr 2024 17:43:31 -0300")

* 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?

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.

I haven't really thought about the proposed locking protocol, sorry.

Thanks,
Florian


  parent reply	other threads:[~2024-04-26  9:44 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 ` Florian Weimer [this message]
2024-04-26 10:14   ` [RFC PATCH 0/1] " Peter Zijlstra
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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