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

[Christoph Hellwig]

On Fri, Mar 14, 2014 at 11:34:31PM -0400, Theodore Ts'o wrote:
> The current virtio block sets a queue depth of 64, which is
> insufficient for very fast devices.  It has been demonstrated that
> with a high IOPS device, using a queue depth of 256 can double the
> IOPS which can be sustained.
> 
> As suggested by Venkatash Srinivas, set the queue depth by default to
> be one half the the device's virtqueue, which is the maximum queue
> depth that can be supported by the channel to the host OS (each I/O
> request requires at least two VQ entries).

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.

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