From: "tj@kernel.org" <tj@kernel.org>
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: "jiangshanlai@gmail.com" <jiangshanlai@gmail.com>,
"mhocko@suse.com" <mhocko@suse.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"juri.lelli@redhat.com" <juri.lelli@redhat.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"vincent.guittot@linaro.org" <vincent.guittot@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"neilb@suse.de" <neilb@suse.de>
Subject: Re: [PATCH rfc] workqueue: honour cond_resched() more effectively.
Date: Mon, 9 Nov 2020 11:10:07 -0500 [thread overview]
Message-ID: <20201109161007.GF7496@mtj.duckdns.org> (raw)
In-Reply-To: <d2c79d91e29134ef6184138de5fc856ca530d2a5.camel@hammerspace.com>
Hello,
On Mon, Nov 09, 2020 at 02:11:42PM +0000, Trond Myklebust wrote:
> That means changing all filesystem code to use cpu-intensive queues. As
> far as I can tell, they all use workqueues (most of them using the
> standard system queue) for fput(), dput() and/or iput() calls.
I suppose the assumption was that those operations couldn't possiby be
expensive enough to warrant other options, which doesn't seem to be the case
unfortunately. Switching the users to system_unbound_wq, which should be
pretty trivial, seems to be the straight forward solution.
I can definitely see benefits in making workqueue smarter about
concurrency-managed work items taking a long time. Given that nothing on
these types of workqueues can be latency sensitive and the problem being
reported is on the scale of tens of seconds, I think a more palatable
approach could be through watchdog mechanism rather than hooking into
cond_resched(). Something like:
* Run watchdog timer more frequently - e.g. 1/4 of threshold.
* If a work item is occupying the local concurrency for too long, set
WORKER_CPU_INTENSIVE for the worker and, probably, generate a warning.
I still think this should generate a warning and thus can't replace
switching to unbound wq. The reason is that the concurrency limit isn't the
only problem. A kthread needing to run on one particular CPU for tens of
seconds just isn't great.
Thanks.
--
tejun
next prev parent reply other threads:[~2020-11-09 16:10 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-09 2:54 [PATCH rfc] workqueue: honour cond_resched() more effectively NeilBrown
2020-11-09 7:50 ` Michal Hocko
2020-11-09 8:00 ` Peter Zijlstra
2020-11-09 13:50 ` Trond Myklebust
2020-11-09 14:01 ` tj
2020-11-09 14:11 ` Trond Myklebust
2020-11-09 16:10 ` tj [this message]
2020-11-17 22:16 ` NeilBrown
[not found] ` <20201118025820.307-1-hdanton@sina.com>
2020-11-18 5:11 ` NeilBrown
[not found] ` <20201118055108.358-1-hdanton@sina.com>
2020-11-19 23:07 ` NeilBrown
2020-12-02 20:20 ` tj
[not found] ` <20201120025953.607-1-hdanton@sina.com>
2020-11-20 4:33 ` NeilBrown
[not found] ` <20201126100646.1790-1-hdanton@sina.com>
2020-11-26 23:44 ` NeilBrown
2020-11-19 23:23 ` NeilBrown
2020-11-25 12:36 ` tj
2020-11-26 23:30 ` NeilBrown
2020-11-09 14:20 ` Peter Zijlstra
2020-11-10 2:26 ` NeilBrown
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