Messages in this thread | | | Date | Thu, 18 Oct 2012 14:54:03 -0500 | From | Nathan Zimmer <> | Subject | Re: [PATCH] procfs: Improve Scaling in proc |
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On 10/18/2012 02:46 AM, Eric Dumazet wrote: > On Wed, 2012-10-17 at 15:25 -0500, Nathan Zimmer wrote: >> I am currently tracking a hotlock reported by a customer on a large, 512 cores, >> system, I am currently running 3.7.0 rc1 but the issue looks like it has been >> this way for a very long time. >> The offending lock is proc_dir_entry->pde_unload_lock. >> >> This patch converts the replaces the lock with the rcu. It is a refresh of what >> was orignally suggested by Eric Dumazet. I refreshed it to the 3.7. >> >> Supporting numbers, lower is better, they are from the test I posted earlier. >> cpuinfo baseline Rcu >> tasks read-sec read-sec >> 1 0.0141 0.0141 >> 2 0.0140 0.0142 >> 4 0.0140 0.0141 >> 8 0.0145 0.0140 >> 16 0.0553 0.0168 >> 32 0.1688 0.0549 >> 64 0.5017 0.1690 >> 128 1.7005 0.5038 >> 256 5.2513 2.0804 >> 512 8.0529 3.0162 >> >> >> Cc: Eric Dumazet <eric.dumazet@gmail.com> >> Cc: Alexander Viro <viro@zeniv.linux.org.uk> >> Cc: David Woodhouse <dwmw2@infradead.org> >> Cc: Alexey Dobriyan <adobriyan@gmail.com> >> Signed-off-by: Nathan Zimmer <nzimmer@sgi.com> > > Hmm, this patch had several issues and I had no time yet to work on a > new version. I probably wont have time in a near future. > > Paul sent me some comments about it, I hope he doesnt mind I copy them > here, if you want to polish the patch. > > Thanks !
I'll try to polish this up and resend it. And any comments are most welcome.
> On Wed, 2012-10-03 at 10:56 -0700, Paul E. McKenney wrote: >> Finally getting back to this... :-/ >> >> Why not set the initial value of the reference counter to 1 >> (rather than zero), continue acquiring with atomic_inc(), but >> use atomic_dec_and_test() to decrement? Put a completion in >> the data structure, so if the atomic_dec_and_test() indicates that >> the counter is now zero, do a complete(). >> >> Then to free the object, remove it from the data structure, do a >> synchronize_rcu(), do an atomic_dec_and_test() to remove the initial >> value, again doing a complete() if the counter is now zero. The do >> a wait_for_completion(). >> >> This would get rid of the polling loop. >> >> So, what am I missing here? ;-) >> >> Thanx, Paul >>
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