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Re: [RFC PATCH v7 1/7] Restartable sequences system call

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC PATCH v7 1/7] Restartable sequences system call
Date 2016-08-03 14:30 +0200
Message-ID <s23t8-2tz-17@gated-at.bofh.it> (permalink)
References <rXtxT-4A4-3@gated-at.bofh.it> <rXtxU-4A4-31@gated-at.bofh.it> <rYXax-2Cq-1@gated-at.bofh.it> <rZ0UN-53b-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, Jul 26, 2016 at 03:02:19AM +0000, Mathieu Desnoyers wrote:
> We really care about preemption here. Every migration implies a
> preemption from a user-space perspective. If we would only care
> about keeping the CPU id up-to-date, hooking into migration would be
> enough. But since we want atomicity guarantees for restartable
> sequences, we need to hook into preemption.

> It allows user-space to perform update operations on per-cpu data without
> requiring heavy-weight atomic operations.

Well, a CMPXCHG without LOCK prefix isn't all that expensive on x86.

It is however on PPC and possibly other architectures, so in name of
simplicity supporting only the one variant makes sense.

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Thread

Re: [RFC PATCH v7 1/7] Restartable sequences system call Andy Lutomirski <luto@amacapital.net> - 2016-07-26 01:10 +0200
  Re: [RFC PATCH v7 1/7] Restartable sequences system call Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-07-26 05:10 +0200
    Re: [RFC PATCH v7 1/7] Restartable sequences system call Peter Zijlstra <peterz@infradead.org> - 2016-08-03 14:30 +0200
      Re: [RFC PATCH v7 1/7] Restartable sequences system call Andy Lutomirski <luto@amacapital.net> - 2016-08-03 18:50 +0200
        Re: [RFC PATCH v7 1/7] Restartable sequences system call Christoph Lameter <cl@linux.com> - 2016-08-03 20:40 +0200
          Re: [RFC PATCH v7 1/7] Restartable sequences system call Andy Lutomirski <luto@amacapital.net> - 2016-08-04 07:10 +0200
        Re: [RFC PATCH v7 1/7] Restartable sequences system call Boqun Feng <boqun.feng@gmail.com> - 2016-08-04 06:30 +0200
          Re: [RFC PATCH v7 1/7] Restartable sequences system call Andy Lutomirski <luto@amacapital.net> - 2016-08-04 07:20 +0200
            Re: [RFC PATCH v7 1/7] Restartable sequences system call Boqun Feng <boqun.feng@gmail.com> - 2016-08-09 18:20 +0200
              Re: [RFC PATCH v7 1/7] Restartable sequences system call Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-08-10 20:20 +0200
              Re: [RFC PATCH v7 1/7] Restartable sequences system call Andy Lutomirski <luto@amacapital.net> - 2016-08-10 21:10 +0200
              Re: [RFC PATCH v7 1/7] Restartable sequences system call Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-08-10 22:50 +0200
            Re: [RFC PATCH v7 1/7] Restartable sequences system call Andy Lutomirski <luto@amacapital.net> - 2016-08-10 21:40 +0200
    Re: [RFC PATCH v7 1/7] Restartable sequences system call Christoph Lameter <cl@linux.com> - 2016-08-03 20:40 +0200
      Re: [RFC PATCH v7 1/7] Restartable sequences system call Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-08-10 22:10 +0200
        Re: [RFC PATCH v7 1/7] Restartable sequences system call Christoph Lameter <cl@linux.com> - 2016-08-10 22:40 +0200

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