linux-kernel - Re: [PATCH v4 2/2] virtio_balloon: Use a workqueue instead of "vballoon" kthread

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Message-ID: <20160103135839.GF3660@htj.duckdns.org>
Date:	Sun, 3 Jan 2016 08:58:39 -0500
From:	Tejun Heo <tj@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Petr Mladek <pmladek@...e.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeff Epler <jepler@...ythonic.net>,
	Jiri Kosina <jkosina@...e.cz>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.cz>
Subject: Re: [PATCH v4 2/2] virtio_balloon: Use a workqueue instead of
 "vballoon" kthread

Hello, Michael.

On Sat, Jan 02, 2016 at 11:36:03PM +0200, Michael S. Tsirkin wrote:
> > Why so?  As long as the maximum concurrently used workers are not
> > high, 1/5 second or even a lot longer sleeps are completely fine.
> 
> I always thought the right way to defer executing a work queue item
> is to queue delayed work, not sleep + queue work.

That works too and is preferable if there are gonna be a lot of work
items sleeping but it isn't different from any other blocking.

> Doing a sleep ties up one thread for 1/5 of a second, does it not?

It does.

> If so, as long as it's the only driver doing this, we'll be fine,
> but if many others copy this pattern, things will
> start to break, will they not?

The maximum concurrency on the system_wq is 256 which is pretty high,
so for most use cases, it's fine.  If high concurrency is expected,
it's better to break it out to a separate workqueue.

Thanks.

-- 
tejun
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