Hello Mathieu On 12 December 2015 at 13:40, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > ----- On Dec 11, 2015, at 1:56 PM, Michael Kerrisk mtk.manpages@xxxxxxxxx wrote: > >> Hi Mathieu, >> >> On 12/10/2015 04:39 PM, Mathieu Desnoyers wrote: >>> Expose a new system call allowing threads to register a userspace memory >>> area where to store the current CPU number. Scheduler migration sets the >>> TIF_NOTIFY_RESUME flag on the current thread. Upon return to user-space, >>> a notify-resume handler updates the current CPU value within that >>> user-space memory area. >>> >>> This getcpu cache is an alternative to the sched_getcpu() vdso which has >>> a few benefits: >>> - It is faster to do a memory read that to call a vDSO, >>> - This cached value can be read from within an inline assembly, which >>> makes it a useful building block for restartable sequences. >>> >>> This approach is inspired by Paul Turner and Andrew Hunter's work >>> on percpu atomics, which lets the kernel handle restart of critical >>> sections: >>> Ref.: >>> * https://lkml.org/lkml/2015/6/24/665 >>> * https://lwn.net/Articles/650333/ >>> * >>> http://www.linuxplumbersconf.org/2013/ocw/system/presentations/1695/original/LPC%20-%20PerCpu%20Atomics.pdf >>> >>> Benchmarking sched_getcpu() vs tls cache approach. Getting the >>> current CPU number: >> >> Is there a man page for this system call? > > Hi Michael, > > Not yet. I first want check whether the overall technical > approach is deemed acceptable before adding documentation. > > Adding a manpage is going to be one of the first steps after > we agree on the syscall interface. Or perhaps you are suggesting > that adding a manpage at this RFC stage could help the > interface discussion ? Yup, that's exactly what I'm suggesting. Thanks, Michael -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
