On Mon 09-09-19 08:11:36, Alexander Duyck wrote: > On Mon, 2019-09-09 at 10:14 +0200, David Hildenbrand wrote: > > On 07.09.19 19:25, Alexander Duyck wrote: > > > From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> > > > > > > Change the logic used to generate randomness in the suffle path so that we > > > can avoid cache line bouncing. The previous logic was sharing the offset > > > and entropy word between all CPUs. As such this can result in cache line > > > bouncing and will ultimately hurt performance when enabled. > > > > So, usually we perform such changes if there is real evidence. Do you > > have any such performance numbers to back your claims? > > I'll have to go rerun the test to get the exact numbers. The reason this > came up is that my original test was spanning NUMA nodes and that made > this more expensive as a result since the memory was both not local to the > CPU and was being updated by multiple sockets. What was the pattern of page freeing in your testing? I am wondering because order 0 pages should be prevailing and those usually go via pcp lists so they do not get shuffled unless the batch is full IIRC. -- Michal Hocko SUSE Labs
