From: Roman Penyaev <rpenyaev@suse.de>
To: Jason Baron <jbaron@akamai.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/1] epoll: use rwlock in order to reduce ep_poll_callback() contention
Date: Wed, 05 Dec 2018 21:11:54 +0100 [thread overview]
Message-ID: <1c214a8b9e6c06589c912b55d2ef5f37@suse.de> (raw)
In-Reply-To: <b8c6ef78-f0ea-2bc5-566a-9482061fffb2@akamai.com>
On 2018-12-05 17:38, Jason Baron wrote:
>
> I think it might be interesting for, at least testing, to see if not
> grabbing
> wq.lock improves your benchmarks any further? fwiw, epoll only recently
> started
> grabbing wq.lock bc lockdep required it.
That's easy! I've just tested with the following hunk applied to my
patch on top:
+++ b/fs/eventpoll.c
@@ -1228,7 +1228,7 @@ static int ep_poll_callback(wait_queue_entry_t
*wait, unsigned mode, int sync, v
break;
}
}
- wake_up(&ep->wq);
+ wake_up_locked(&ep->wq);
}
Run time:
threads w/ wq.lock w/o wq.lock
------- ---------- -----------
8 8581ms 8602ms
16 13800ms 13715ms
32 24167ms 23817ms
No big difference. According to perf the contention is on read lock and
on try_to_wake_up(), the p->pi_lock, which serializes access exactly
like
vanished wq.lock.
- 24.41% 5.39% a.out [kernel.kallsyms] [k] ep_poll_callback
- 19.02% ep_poll_callback
+ 11.88% _raw_read_lock_irqsave
+ 5.74% _raw_read_unlock_irqrestore
- 1.39% __wake_up_common
- 1.22% try_to_wake_up
+ 0.98% _raw_spin_lock_irqsave
--
Roman
next prev parent reply other threads:[~2018-12-05 20:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 11:02 [RFC PATCH 1/1] epoll: use rwlock in order to reduce ep_poll_callback() contention Roman Penyaev
2018-12-03 17:34 ` Linus Torvalds
2018-12-04 11:50 ` Roman Penyaev
2018-12-04 23:59 ` Andrea Parri
2018-12-05 11:25 ` Roman Penyaev
2018-12-04 17:23 ` Jason Baron
2018-12-04 19:02 ` Paul E. McKenney
2018-12-05 11:22 ` Roman Penyaev
2018-12-05 11:16 ` Roman Penyaev
2018-12-05 16:38 ` Jason Baron
2018-12-05 20:11 ` Roman Penyaev [this message]
2018-12-06 1:54 ` Davidlohr Bueso
2018-12-06 3:08 ` Davidlohr Bueso
2018-12-06 10:27 ` Roman Penyaev
2018-12-06 4:04 ` Davidlohr Bueso
2018-12-06 10:25 ` Roman Penyaev
2018-12-05 23:46 ` Eric Wong
2018-12-06 10:52 ` Roman Penyaev
2018-12-06 20:35 ` Eric Wong
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