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Message-ID: <20171214194853.GE3326@worktop> Date: Thu, 14 Dec 2017 20:48:53 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Christopher Lameter <cl@...ux.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Boqun Feng <boqun.feng@...il.com>, Andy Lutomirski <luto@...capital.net>, Dave Watson <davejwatson@...com>, linux-kernel <linux-kernel@...r.kernel.org>, linux-api <linux-api@...r.kernel.org>, Paul Turner <pjt@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Russell King <linux@....linux.org.uk>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>, Andi Kleen <andi@...stfloor.org>, Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>, Josh Triplett <josh@...htriplett.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Michael Kerrisk <mtk.manpages@...il.com>, Alexander Viro <viro@...iv.linux.org.uk> Subject: Re: [RFC PATCH for 4.16 02/21] rseq: Introduce restartable sequences system call (v12) On Thu, Dec 14, 2017 at 12:50:13PM -0600, Christopher Lameter wrote: > Ultimately I wish fast increments like done by this_cpu_inc() could be > implemented in an efficient way on non x86 platforms that do not have > cheap instructions like that. So the problem isn't migration; for that we could wrap the operation in preempt_disable() which is not more expensive than rseq would be. And a lot more deterministic. The problem instead is interrupts, which can result in nested load-store operations, and that comes apart. This then means having to disable interrupts over these things and _that_ is expensive.
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