On Tue 22-12-20 22:42:13, Liang Li wrote: > > > ===================================================== > > > QEMU use 4K pages, THP is off > > > round1 round2 round3 > > > w/o this patch: 23.5s 24.7s 24.6s > > > w/ this patch: 10.2s 10.3s 11.2s > > > > > > QEMU use 4K pages, THP is on > > > round1 round2 round3 > > > w/o this patch: 17.9s 14.8s 14.9s > > > w/ this patch: 1.9s 1.8s 1.9s > > > ===================================================== > > > > The cost of zeroing pages has to be paid somewhere. You've successfully > > moved it out of this path that you can measure. So now you've put it > > somewhere that you're not measuring. Why is this a win? > > Win or not depends on its effect. For our case, it solves the issue > that we faced, so it can be thought as a win for us. If others don't > have the issue we faced, the result will be different, maybe they will > be affected by the side effect of this feature. I think this is your > concern behind the question. right? I will try to do more tests and > provide more benchmark performance data. Yes, zeroying memory does have a noticeable overhead but we cannot simply allow tasks to spil over this overhead to all other users by default. So if anything this would need to be an opt-in feature configurable by administrator. -- Michal Hocko SUSE Labs
