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@dachary.org> 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/21...
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-- Loïc Dachary, Artisan Logiciel Libre
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