Loic,
Here is some discussion on cache false sharing that you may find valuable: https://github.com/ceph/ceph/pull/9431 .
Maybe it is possible to turn perf c2c into some systemic check?
Best regards,
Adam
On Tue, 16 Mar 2021 at 22:59, Loïc Dachary <loic@xxxxxxxxxxx> wrote:
On 16/03/2021 22:01, Mark Nelson wrote:
> Hi Loïc,
>
>
> I don't have any tests specifically for this, but looking at #39057, I wonder if something could be crafted using the check_shard_select test that Adam wrote as a template. What do you think?
That sounds like a good idea. And maybe using cachegrind[0] also?
[0] https://www.valgrind.org/docs/manual/cg-manual.html
>
>
> Mark
>
>
> On 3/16/21 3:52 PM, Loïc Dachary wrote:
>> Hi Mark,
>>
>> While trying to figure out a random failure in the mempool tests[0] introduced when fixing a bug in how mempool selects shards holding the byte count of a given pool[1] earlier this year, I was intrigued by this "cache line ping pong" problem[2]. And I wonder if you have some kind of benchmark, somewhere in your toolbox, that someone could use to demonstrate the problem. Maybe such a code could be adapted to show the benefit of the optimization implemented in mempool?
>>
>> Cheers
>>
>> [0] https://tracker.ceph.com/issues/49781#note-9
>> [1] https://github.com/ceph/ceph/pull/39057/files
>> [2] https://www.drdobbs.com/parallel/understanding-and-avoiding-memory-issues/212400410
>>
>>
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--
Loïc Dachary, Artisan Logiciel Libre
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