Re: [PATCH v2] perf/core: Add support for PMUs that can be read from more than 1 CPU

[Saravana Kannan]

On 03/05/2018 04:21 AM, Mark Rutland wrote:
On Mon, Mar 05, 2018 at 12:17:02PM +0000, Mark Rutland wrote:
On Fri, Mar 02, 2018 at 05:14:53PM -0800, Saravana Kannan wrote:

@@ -629,6 +629,7 @@ struct perf_event {

        int                             oncpu;
        int                             cpu;
+       cpumask_t                       readable_on_cpus;

For most PMUs, this will be emptry, and it's potentially *very* large
(e.g. on systems where NR_CPUS is 4096). Please use a poitner to a mask,
as I suggested in [1], e.g.

[1] 
https://lkml.kernel.org/r/20171128124534.3jvuala525wvn...@wfg-t540p.sh.intel.com

Whoops, that should've been:

[1] https://lkml.kernel.org/r/20180225143802.denbkubqjg2dc7af@salmiak


I didn't notice you mentioned the use of pointers, but I was planning on 
doing that anyway. But then I realize people will complain about 
cacheline bouncing across 4096 CPUs if I use a cpu mask pointer.

Thanks,
Saravana

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