From: Christopher Lameter <cl@linux.com>
To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Dave Watson <davejwatson@fb.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
Paul Turner <pjt@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King <linux@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
Andrew Hunter <ahh@google.com>, Andi Kleen <andi@firstfloor.org>,
Ben Maurer <bmaurer@fb.com>, Steven Rostedt <rostedt@goodmis.org>,
Josh Triplett <josh@joshtriplett.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Catalin Marinas <catalin.>
Subject: Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12)
Date: Mon, 2 Apr 2018 10:03:58 -0500 (CDT) [thread overview]
Message-ID: <alpine.DEB.2.20.1804021000290.23911@nuc-kabylake> (raw)
In-Reply-To: <20180401171356.085a2a33@alans-desktop>
On Sun, 1 Apr 2018, Alan Cox wrote:
> > Restartable sequences are atomic with respect to preemption
> > (making it atomic with respect to other threads running on the
> > same CPU), as well as signal delivery (user-space execution
> > contexts nested over the same thread).
>
> CPU generally means 'big lump with legs on it'. You are not atomic to the
> same CPU, because that CPU may have 30+ cores with 8 threads per core.
>
> It could do with some better terminology (hardware thread, CPU context ?)
Well we call it a "CPU" in the scheduler context I think. We could use
better terminology throughout the kernel tools and source.
Hardware Execution Context?
> > In a typical usage scenario, the thread registering the rseq
> > structure will be performing loads and stores from/to that
> > structure. It is however also allowed to read that structure
> > from other threads. The rseq field updates performed by the
> > kernel provide relaxed atomicity semantics, which guarantee
> > that other threads performing relaxed atomic reads of the cpu
> > number cache will always observe a consistent value.
>
> So what happens to your API if the kernel atomics get improved ? You are
> effectively exporting rseq behaviour from private to public.
There is already a pretty complex coherency model guiding kernel atomics.
Improvements/changes to that are difficult and the effect will ripple
throughout the kernel. So I would suggest that these areas of the kernel
are pretty "petrified" (or written in stone).
next prev parent reply other threads:[~2018-04-02 15:03 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-27 16:05 [RFC PATCH for 4.17 00/21] Restartable sequences and CPU op vector Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 01/21] uapi headers: Provide types_32_64.h Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12) Mathieu Desnoyers
2018-03-28 6:47 ` Boqun Feng
2018-03-28 14:06 ` Mathieu Desnoyers
2018-03-28 14:31 ` Mathieu Desnoyers
2018-03-28 11:19 ` Peter Zijlstra
2018-03-28 14:19 ` Mathieu Desnoyers
2018-03-28 11:22 ` Peter Zijlstra
2018-03-28 14:26 ` Mathieu Desnoyers
2018-03-28 12:29 ` Peter Zijlstra
2018-03-28 12:52 ` Peter Zijlstra
2018-03-28 15:03 ` Mathieu Desnoyers
2018-03-28 16:19 ` Mathieu Desnoyers
2018-03-28 12:50 ` Peter Zijlstra
2018-03-28 14:47 ` Mathieu Desnoyers
2018-03-28 14:59 ` Peter Zijlstra
2018-03-28 15:14 ` Mathieu Desnoyers
2018-03-28 15:28 ` Peter Zijlstra
2018-03-28 15:37 ` Mathieu Desnoyers
2018-03-28 17:49 ` Peter Zijlstra
2018-03-28 20:19 ` Mathieu Desnoyers
2018-03-28 21:25 ` Thomas Gleixner
2018-03-29 13:54 ` Mathieu Desnoyers
2018-03-29 14:23 ` Peter Zijlstra
2018-03-29 15:39 ` Mathieu Desnoyers
2018-03-29 16:24 ` Steven Rostedt
2018-03-29 18:02 ` Mathieu Desnoyers
2018-03-29 18:07 ` Steven Rostedt
2018-03-29 18:35 ` Mathieu Desnoyers
2018-03-29 18:46 ` Steven Rostedt
2018-03-29 18:47 ` Steven Rostedt
2018-04-01 16:13 ` Alan Cox
2018-04-02 15:03 ` Christopher Lameter [this message]
2018-04-02 15:27 ` Paul E. McKenney
2018-04-02 15:33 ` Mathieu Desnoyers
2018-04-03 16:36 ` Mathieu Desnoyers
2018-04-03 20:32 ` Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 03/21] arm: Add restartable sequences support Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 04/21] arm: Wire up restartable sequences system call Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 05/21] x86: Add support for restartable sequences Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 06/21] x86: Wire up restartable sequence system call Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 07/21] powerpc: Add support for restartable sequences Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 08/21] powerpc: Wire up restartable sequences system call Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 09/21] sched: Implement push_task_to_cpu (v2) Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 10/21] cpu_opv: Provide cpu_opv system call (v6) Mathieu Desnoyers
2018-03-28 15:22 ` Peter Zijlstra
2018-03-28 17:54 ` Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 11/21] x86: Wire up cpu_opv system call Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 12/21] powerpc: " Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 13/21] arm: " Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 14/21] selftests: lib.mk: Introduce OVERRIDE_TARGETS Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 15/21] cpu_opv: selftests: Implement selftests (v7) Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 16/21] rseq: selftests: Provide rseq library (v5) Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 17/21] rseq: selftests: Provide percpu_op API Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 18/21] rseq: selftests: Provide basic test Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 19/21] rseq: selftests: Provide basic percpu ops test Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 20/21] rseq: selftests: Provide parametrized tests Mathieu Desnoyers
2018-03-27 16:05 ` [RFC PATCH for 4.17 21/21] rseq: selftests: Provide Makefile, scripts, gitignore Mathieu Desnoyers
2018-03-27 19:09 ` [RFC PATCH for 4.17 00/21] Restartable sequences and CPU op vector Peter Zijlstra
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