linux-kernel - Re: [PATCH] virtio-blk: make the queue depth the max supportable by the hypervisor

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Message-ID: <20140315151322.GA17270@thunk.org>
Date:	Sat, 15 Mar 2014 11:13:22 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Venkatesh Srinivas <venkateshs@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	virtio-dev@...ts.oasis-open.org,
	virtualization@...ts.linux-foundation.org,
	Frank Swiderski <fes@...gle.com>
Subject: Re: [PATCH] virtio-blk: make the queue depth the max supportable by
 the hypervisor

On Sat, Mar 15, 2014 at 06:57:23AM -0700, Christoph Hellwig wrote:
> I don't think this should be a module parameter.  The default sizing
> should be based of the parameters of the actual virtqueue, and if we
> want to allow tuning it it should be by a sysfs attribute, preferable
> using the same semantics as SCSI.

I wanted that too, but looking at the multiqueue code, it wasn't all
obvious how to safely adjust the queue depth once the virtio-blk
device driver is initialized and becomes active.  There are all sorts
data structures including bitmaps, etc. that would have to be resized,
and I decided it would be too difficult / risky for me to make it be
dynamically resizeable.

So I settled on a module parameter thinking it would mostly only used
by testers / benchmarkers.

Can someone suggest a way to do a dynamic resizing of the virtio-blk
queue depth easily / safely?

    	    	      	     	- Ted
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