Quoting Janis Schoetterl-Glausch (2022-11-16 20:36:46) > On Wed, 2022-11-02 at 15:12 +0100, Heiko Carstens wrote: > > > [...] > > > I also did not limit the number of retries for the one and two byte > > scenarion. Before doing that we need to have proof that there really is a > > problem. Maybe Nico or you will give this a try. > > I wrote a memop selftest testcase where the main thread uses the one byte cmpxchg > while n vcpus flip adjacent bits. The time the test case runs increases superlinearly with n. > With 248 vcpus, 1000 one byte cmpxchgs take 25s. > I'm not sure how meaningful the test is since the worst case would be if the threads hammering > the word would run on a cpu dedicated to them. > > In any case, why not err on the side of caution and limit the iterations? > I'll send an rfc patch. I agree, limiting sounds like the safe choice.
