Re: [PATCH] procfs: Improve Scaling in proc
From: Eric Dumazet
Date: Thu Oct 18 2012 - 03:46:33 EST
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@xxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Signed-off-by: Nathan Zimmer <nzimmer@xxxxxxx>
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.
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
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/