From: Tejun Heo <tj@kernel.org>
To: Jeff Layton <jlayton@redhat.com>
Cc: torvalds@linux-foundation.org, mingo@elte.hu,
peterz@infradead.org, awalls@radix.net,
linux-kernel@vger.kernel.org, jeff@garzik.org,
akpm@linux-foundation.org, jens.axboe@oracle.com,
rusty@rustcorp.com.au, cl@linux-foundation.org,
dhowells@redhat.com, arjan@linux.intel.com, avi@redhat.com,
johannes@sipsolutions.net, andi@firstfloor.org,
Steve French <sfrench@samba.org>
Subject: Re: [PATCH 38/40] cifs: use workqueue instead of slow-work
Date: Wed, 20 Jan 2010 10:23:50 +0900 [thread overview]
Message-ID: <4B565B26.3060709@kernel.org> (raw)
In-Reply-To: <20100119195641.7b6a17e4@tlielax.poochiereds.net>
On 01/20/2010 09:56 AM, Jeff Layton wrote:
>> Hmmm... Why is locking GlobalSMBSeslock necessary?
>> cifs_oplock_break_get() can never fail and it seems that
>> is_valid_oplock_break() should be holding valid reference by the time
>> it enqueues the work, so wouldn't the following be sufficient?
>>
>> if (queue_work(system_single_wq, &netfile->oplock_break))
>> cifs_oplock_break_get(netfile);
>>
>
> I guess I wasn't sure I could count on that. It seems unlikely that the
> work would run before you did the "get", but unlikely races are even
> harder to troubleshoot when they do get hit.
>
> FWIW, it's not a terribly hot codepath, so taking and dropping the
> spinlock shouldn't be too bad for performance. If you're certain that
> we don't need to worry about it though, then maybe we can just skip
> doing that.
Oooh, I don't know the code very well and can't guarantee any of that.
Ah, okay, I was confused. Work can run and finish before the
reference is incremented. So, yeap, I'll add the spinlocking in the
work function.
>>> Also, this change seems to have changed the logic a bit. The
>>> oplock_break_cancelled flag is being set to false unconditionally, and
>>> the printk was dropped. Not a big deal on the last part, but we can't
>>> really do much with errors in this codepath so it might be helpful to
>>> have some indication that there are problems here.
>>
>> The thing is that slow_work_enqueue() can only fail if getting a
>> reference fails. In cifs' case, it always succeeds so there's no
>> failure case to handle there.
>>
>
> Ok, but here we're changing this to queue_work. Is that also guaranteed
> to succeed here? If so, then dropping the printk is fine. If not, then
> I think we should keep it in.
Yeap, queue_work() is guaranteed to succeed. The only possible
outcomes are 1. queued or 2. is already queued.
> It's been a while since I overhauled this code, so I'll need to look
> again at the semantics for the oplock_break_cancelled flag. It may be
> ok to just set it unconditionally like this, but I'll need to check
> and be sure.
Thanks.
--
tejun
next prev parent reply other threads:[~2010-01-20 1:19 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-18 0:57 [PATCHSET] concurrency managed workqueue, take#3 Tejun Heo
2010-01-18 0:57 ` [PATCH 01/40] sched: consult online mask instead of active in select_fallback_rq() Tejun Heo
2010-01-18 10:13 ` Peter Zijlstra
2010-01-18 11:26 ` Tejun Heo
2010-01-18 0:57 ` [PATCH 02/40] sched: rename preempt_notifiers to sched_notifiers and refactor implementation Tejun Heo
2010-01-18 0:57 ` [PATCH 03/40] sched: refactor try_to_wake_up() Tejun Heo
2010-01-18 0:57 ` [PATCH 04/40] sched: implement __set_cpus_allowed() Tejun Heo
2010-01-18 9:56 ` Peter Zijlstra
2010-01-18 11:22 ` Tejun Heo
2010-01-18 11:41 ` Peter Zijlstra
2010-01-19 1:07 ` Tejun Heo
2010-01-19 8:37 ` Peter Zijlstra
2010-01-20 8:35 ` Tejun Heo
2010-01-20 8:50 ` Peter Zijlstra
2010-01-20 9:00 ` Tejun Heo
2010-01-20 8:59 ` Peter Zijlstra
2010-01-24 8:18 ` Tejun Heo
2010-01-18 0:57 ` [PATCH 05/40] sched: make sched_notifiers unconditional Tejun Heo
2010-01-18 0:57 ` [PATCH 06/40] sched: add wakeup/sleep sched_notifiers and allow NULL notifier ops Tejun Heo
2010-01-18 9:57 ` Peter Zijlstra
2010-01-18 11:31 ` Tejun Heo
2010-01-18 12:49 ` Peter Zijlstra
2010-01-19 1:04 ` Tejun Heo
2010-01-19 8:28 ` Tejun Heo
2010-01-19 8:55 ` Peter Zijlstra
2010-01-20 8:47 ` Tejun Heo
2010-01-18 0:57 ` [PATCH 07/40] sched: implement try_to_wake_up_local() Tejun Heo
2010-01-18 0:57 ` [PATCH 08/40] acpi: use queue_work_on() instead of binding workqueue worker to cpu0 Tejun Heo
2010-01-18 0:57 ` [PATCH 09/40] stop_machine: reimplement without using workqueue Tejun Heo
2010-01-18 0:57 ` [PATCH 10/40] workqueue: misc/cosmetic updates Tejun Heo
2010-01-18 0:57 ` [PATCH 11/40] workqueue: merge feature parameters into flags Tejun Heo
2010-01-18 0:57 ` [PATCH 12/40] workqueue: define both bit position and mask for work flags Tejun Heo
2010-01-18 0:57 ` [PATCH 13/40] workqueue: separate out process_one_work() Tejun Heo
2010-01-18 0:57 ` [PATCH 14/40] workqueue: temporarily disable workqueue tracing Tejun Heo
2010-01-18 0:57 ` [PATCH 15/40] workqueue: kill cpu_populated_map Tejun Heo
2010-01-18 0:57 ` [PATCH 16/40] workqueue: update cwq alignement Tejun Heo
2010-01-18 0:57 ` [PATCH 17/40] workqueue: reimplement workqueue flushing using color coded works Tejun Heo
2010-01-18 0:57 ` [PATCH 18/40] workqueue: introduce worker Tejun Heo
2010-01-18 0:57 ` [PATCH 19/40] workqueue: reimplement work flushing using linked works Tejun Heo
2010-01-18 0:57 ` [PATCH 20/40] workqueue: implement per-cwq active work limit Tejun Heo
2010-01-18 0:57 ` [PATCH 21/40] workqueue: reimplement workqueue freeze using max_active Tejun Heo
2010-01-18 0:57 ` [PATCH 22/40] workqueue: introduce global cwq and unify cwq locks Tejun Heo
2010-01-18 0:57 ` [PATCH 23/40] workqueue: implement worker states Tejun Heo
2010-01-18 0:57 ` [PATCH 24/40] workqueue: reimplement CPU hotplugging support using trustee Tejun Heo
2010-01-18 0:57 ` [PATCH 25/40] workqueue: make single thread workqueue shared worker pool friendly Tejun Heo
2010-01-18 0:57 ` [PATCH 26/40] workqueue: use shared worklist and pool all workers per cpu Tejun Heo
2010-01-18 0:57 ` [PATCH 27/40] workqueue: implement concurrency managed dynamic worker pool Tejun Heo
2010-01-18 0:57 ` [PATCH 28/40] workqueue: increase max_active of keventd and kill current_is_keventd() Tejun Heo
2010-01-18 0:57 ` [PATCH 29/40] workqueue: add system_wq and system_single_wq Tejun Heo
2010-01-18 0:57 ` [PATCH 30/40] workqueue: implement work_busy() Tejun Heo
2010-01-18 2:52 ` Andy Walls
2010-01-18 5:41 ` Tejun Heo
2010-01-18 0:57 ` [PATCH 31/40] libata: take advantage of cmwq and remove concurrency limitations Tejun Heo
2010-01-18 15:48 ` Stefan Richter
2010-01-19 0:49 ` Tejun Heo
2010-01-18 0:57 ` [PATCH 32/40] async: introduce workqueue based alternative implementation Tejun Heo
2010-01-18 6:01 ` Arjan van de Ven
2010-01-18 8:49 ` Tejun Heo
2010-01-18 15:25 ` Arjan van de Ven
2010-01-19 0:57 ` Tejun Heo
2010-01-19 0:57 ` Arjan van de Ven
2010-01-19 7:56 ` Tejun Heo
2010-01-19 14:37 ` Arjan van de Ven
2010-01-20 0:19 ` Tejun Heo
2010-01-20 0:31 ` Arjan van de Ven
2010-01-20 2:08 ` Tejun Heo
2010-01-20 6:03 ` Arjan van de Ven
2010-01-20 8:24 ` Tejun Heo
2010-01-22 10:59 ` [PATCH] async: use workqueue for worker pool Tejun Heo
2010-01-18 0:57 ` [PATCH 33/40] async: convert async users to use the new implementation Tejun Heo
2010-01-18 0:57 ` [PATCH 34/40] async: kill original implementation Tejun Heo
2010-01-18 0:57 ` [PATCH 35/40] fscache: convert object to use workqueue instead of slow-work Tejun Heo
2010-01-18 0:57 ` [PATCH 36/40] fscache: convert operation " Tejun Heo
2010-01-18 0:57 ` [PATCH 37/40] fscache: drop references to slow-work Tejun Heo
2010-01-18 0:57 ` [PATCH 38/40] cifs: use workqueue instead of slow-work Tejun Heo
2010-01-19 12:20 ` Jeff Layton
2010-01-20 0:15 ` Tejun Heo
2010-01-20 0:56 ` Jeff Layton
2010-01-20 1:23 ` Tejun Heo [this message]
2010-01-22 11:14 ` [PATCH UPDATED " Tejun Heo
2010-01-22 11:45 ` Jeff Layton
2010-01-24 8:25 ` Tejun Heo
2010-01-24 12:13 ` Jeff Layton
2010-01-25 15:25 ` Tejun Heo
2010-01-18 0:57 ` [PATCH 39/40] gfs2: " Tejun Heo
2010-01-18 9:45 ` Steven Whitehouse
2010-01-18 11:24 ` Tejun Heo
2010-01-18 12:07 ` Steven Whitehouse
2010-01-19 1:00 ` Tejun Heo
2010-01-19 8:46 ` [PATCH UPDATED " Tejun Heo
2010-01-18 0:57 ` [PATCH 40/40] slow-work: kill it Tejun Heo
2010-01-18 1:03 ` perf-wq.c used to generate synthetic workload Tejun Heo
2010-01-18 16:13 ` [PATCHSET] concurrency managed workqueue, take#3 Stefan Richter
2010-02-12 18:03 ` [PATCH 35/40] fscache: convert object to use workqueue instead of slow-work David Howells
2010-02-13 5:43 ` Tejun Heo
2010-02-15 15:04 ` David Howells
2010-02-16 3:40 ` Tejun Heo
2010-02-16 3:59 ` Tejun Heo
2010-02-16 18:05 ` David Howells
2010-02-16 23:50 ` Tejun Heo
2010-02-18 11:50 ` David Howells
2010-02-18 12:33 ` Tejun Heo
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