Hi, Linus, Linus Torvalds writes: > On Wed, Aug 10, 2016 at 4:08 PM, Dave Chinner wrote: >> >> That, to me, says there's a change in lock contention behaviour in >> the workload (which we know aim7 is good at exposing). i.e. the >> iomap change shifted contention from a sleeping lock to a spinning >> lock, or maybe we now trigger optimistic spinning behaviour on a >> lock we previously didn't spin on at all. > > Hmm. Possibly. I reacted to the lower cpu load number, but yeah, I > could easily imagine some locking primitive difference too. > >> We really need instruction level perf profiles to understand >> this - I don't have a machine with this many cpu cores available >> locally, so I'm not sure I'm going to be able to make any progress >> tracking it down in the short term. Maybe the lkp team has more >> in-depth cpu usage profiles they can share? > > Yeah, I've occasionally wanted to see some kind of "top-25 kernel > functions in the profile" thing. That said, when the load isn't all > that familiar, the profiles usually are not all that easy to make > sense of either. But comparing the before and after state might give > us clues. I have started perf-profile data collection, will send out the comparison result soon. Best Regards, Huang, Ying