Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 30 Aug 2013 15:52:49 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount |
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On 08/30/2013 03:40 PM, Al Viro wrote: > On Fri, Aug 30, 2013 at 03:20:48PM -0400, Waiman Long wrote: > >> There are more contention in the lglock than I remember for the run >> in 3.10. This is an area that I need to look at. In fact, lglock is >> becoming a problem for really large machine with a lot of cores. We >> have a prototype 16-socket machine with 240 cores under development. >> The cost of doing a lg_global_lock will be very high in that type of >> machine given that it is already high in this 80-core machine. I >> have been thinking about instead of per-cpu spinlocks, we could >> change the locking to per-node level. While there will be more >> contention for lg_local_lock, the cost of doing a lg_global_lock >> will be much lower and contention within the local die should not be >> too bad. That will require either a per-node variable infrastructure >> or simulated with the existing per-cpu subsystem. > Speaking of lglock, there's a low-hanging fruit in that area: we have > no reason whatsoever to put anything but regular files with FMODE_WRITE > on the damn per-superblock list - the *only* thing it's used for is > mark_files_ro(), which will skip everything except those. And since > read opens normally outnumber the writes quite a bit... Could you > try the diff below and see if it changes the picture? files_lglock > situation ought to get better... > >
Sure. I will try that out, but it probably won't help too much in this test case. The perf profile that I sent out in my previous mail is only partial. The actual one for lg_global_lock was:
1.01% reaim [kernel.kallsyms] [k] lg_global_lock | --- lg_global_lock mntput_no_expire mntput __fput ____fput task_work_run do_notify_resume int_signal | |--51.62%-- __shmdt | --48.38%-- __shmctl
So it is the mnput_no_expire() function that is doing all the lg_global_lock() calls.
Regards, Longman
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