On 04/04/2021 20:24, Joe Mario wrote: > Hi Loïc: > Looking further, there is something in those files. It's just one small cacheline, but there is something there. I guess I'm not used to seeing c2c being run on a laptop, nor am I used to seeing so few samples, or even so little in the kernel. > And I apologize for my quick initial mistaken analysis. > > Here's what it looks like is happening. Correct me if I'm wrong. > > In your "without-sharding" version of Ceph, you had 8 threads in the ceph_test_c2c binary all contending for the same lock located at offset 0 in a cacheline. And then, in the "with-sharding" version of Ceph, you changed it so that each thread would act on its own copy of the 4-byte lock. > > Unfortunately, the "with-sharding" version likely didn't help, because all those 8 locks are packed into the same cacheline, with each lock being 4 bytes away from the last one. > If that is true, then you need to rewrite the code such that all the locks are located by themselves in their own cacheline. > > Is the above assumption correct? Yes, absolutely right. I changed the variable to be 128 bytes aligned[0], is it ok? Maybe there is a constant somewhere that provides this number (number of bytes to be "cache aligned") so it is not hard coded? The output is uploaded in ceph-c2c-jmario-2021-04-04-22-13.tar.gz and hopefully looks better. [0] https://lab.fedeproxy.eu/ceph/ceph/-/commit/54f3a4d0ece0e817bf9308617040f8bb32af01a2 P.S. no need to apologize: I'm grateful for the quick feedback on a Sunday :-) > > Also, I'm going to update the "run_c2c_ceph.sh" script I gave you. The "-g" flag isn't working as it should (known issue). > > Joe > > > On Sun, Apr 4, 2021 at 12:21 PM Loïc Dachary <loic@xxxxxxxxxxx <mailto:loic@xxxxxxxxxxx>> wrote: > > I uploaded the /boot/config-5.10.0-5-amd64 file to dropbox.redhat.com <http://dropbox.redhat.com> : it looks like perf is compiled in: > > # > # Kernel Performance Events And Counters > # > CONFIG_PERF_EVENTS=y > > and all the options below are =y (no =n). > > Maybe a module should be loaded ? > > -- Loïc Dachary, Artisan Logiciel Libre
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