From: Thomas Gleixner <tglx@linutronix.de>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: 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>,
"Florian Weimer" <fw@deneb.enyo.de>,
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>,
"André Almeida" <andrealmeid@igalia.com>,
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,
"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
"Florian Weimer" <fweimer@redhat.com>
Subject: Re: [RFC PATCH v2 1/4] rseq: Add sched_state field to struct rseq
Date: Thu, 28 Sep 2023 22:54:12 +0200 [thread overview]
Message-ID: <87o7hmdnnv.ffs@tglx> (raw)
In-Reply-To: <20230529191416.53955-2-mathieu.desnoyers@efficios.com>
On Mon, May 29 2023 at 15:14, Mathieu Desnoyers wrote:
> +/*
> + * rseq_sched_state should be aligned on the cache line size.
> + */
> +struct rseq_sched_state {
> + /*
> + * Version of this structure. Populated by the kernel, read by
> + * user-space.
> + */
> + __u32 version;
> + /*
> + * The state is updated by the kernel. Read by user-space with
> + * single-copy atomicity semantics. This field can be read by any
> + * userspace thread. Aligned on 32-bit. Contains a bitmask of enum
> + * rseq_sched_state_flags. This field is provided as a hint by the
> + * scheduler, and requires that the page holding this state is
> + * faulted-in for the state update to be performed by the scheduler.
> + */
> + __u32 state;
> + /*
> + * Thread ID associated with the thread registering this structure.
> + * Initialized by user-space before registration.
> + */
> + __u32 tid;
> +};
> +
> /*
> * struct rseq is aligned on 4 * 8 bytes to ensure it is always
> * contained within a single cache-line.
> @@ -148,6 +180,15 @@ struct rseq {
> */
> __u32 mm_cid;
>
> + __u32 padding1;
> +
> + /*
> + * Restartable sequences sched_state_ptr field. Initialized by
> + * userspace to the address at which the struct rseq_sched_state is
> + * located. Read by the kernel on rseq registration.
> + */
> + __u64 sched_state_ptr;
> +
Why is this a separate entity instead of being simply embedded into
struct rseq?
Neither the code comment nor the changelog tells anything about that.
If your intention was to provide a solution for process shared futexes
then you completely failed to understand how process shared futexes
work. If not, then please explain why you need a pointer and the
associated hackery to deal with it.
Thanks,
tglx
next prev parent reply other threads:[~2023-09-28 20:54 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-29 19:14 [RFC PATCH v2 0/4] Extend rseq with sched_state_ptr field Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 1/4] rseq: Add sched_state field to struct rseq Mathieu Desnoyers
2023-05-29 19:35 ` Florian Weimer
2023-05-29 19:48 ` Mathieu Desnoyers
2023-05-30 8:20 ` Florian Weimer
2023-05-30 14:25 ` Mathieu Desnoyers
2023-05-30 15:13 ` Mathieu Desnoyers
2023-09-26 20:52 ` Dmitry Vyukov
2023-09-26 23:49 ` Dmitry Vyukov
2023-09-26 23:54 ` Dmitry Vyukov
2023-09-27 4:51 ` Florian Weimer
2023-09-27 15:58 ` Dmitry Vyukov
2023-09-28 8:52 ` Florian Weimer
2023-09-28 14:44 ` Dmitry Vyukov
2023-09-28 14:47 ` Dmitry Vyukov
2023-09-28 10:39 ` Peter Zijlstra
2023-09-28 11:22 ` David Laight
2023-09-28 13:20 ` Mathieu Desnoyers
2023-09-28 14:26 ` Peter Zijlstra
2023-09-28 14:33 ` David Laight
2023-09-28 15:05 ` André Almeida
2023-09-28 14:43 ` Steven Rostedt
2023-09-28 15:51 ` David Laight
2023-10-02 16:51 ` Steven Rostedt
2023-10-02 17:22 ` David Laight
2023-10-02 17:56 ` Steven Rostedt
2023-09-28 20:21 ` Thomas Gleixner
2023-09-28 20:43 ` Mathieu Desnoyers
2023-09-28 20:54 ` Thomas Gleixner [this message]
2023-09-28 22:11 ` Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 2/4] selftests/rseq: Add sched_state rseq field and getter Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 3/4] selftests/rseq: Implement sched state test program Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 4/4] selftests/rseq: Implement rseq_mutex " Mathieu Desnoyers
2023-09-28 19:55 ` Thomas Gleixner
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