Messages in this thread | | | Date | Thu, 25 Feb 2016 18:04:16 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread |
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On Thu, Feb 25, 2016 at 04:55:26PM +0000, Mathieu Desnoyers wrote: > ----- On Feb 25, 2016, at 4:56 AM, Peter Zijlstra peterz@infradead.org wrote: > The restartable sequences are intrinsically designed to work > on per-cpu data, so they need to fetch the current CPU number > within the rseq critical section. This is where the getcpu_cache > system call becomes very useful when combined with rseq: > getcpu_cache allows reading the current CPU number in a > fraction of cycle.
Yes yes, I know how restartable sequences work.
But what I worry about is that they want a cpu number and a sequence number, and for performance it would be very good if those live in the same cacheline.
That means either getcpu needs to grow a seq number, or restartable sequences need to _also_ provide the cpu number.
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