Messages in this thread | | | Date | Thu, 18 Aug 2011 08:10:37 -0700 | From | Avi Kivity <> | Subject | Re: [PATCH] virtio-blk: Add stats VQ to collect information about devices |
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On 08/17/2011 09:38 PM, Sasha Levin wrote: > On Wed, 2011-08-17 at 16:00 -0700, Avi Kivity wrote: > > On 08/16/2011 12:47 PM, Sasha Levin wrote: > > > This patch adds support for an optional stats vq that works similary to the > > > stats vq provided by virtio-balloon. > > > > > > The purpose of this change is to allow collection of statistics about working > > > virtio-blk devices to easily analyze performance without having to tap into > > > the guest. > > > > > > > > > > Why can't you get the same info from the host? i.e. read sectors? > > Some of the stats you can collect from the host, but some you can't. > > The ones you can't include all the timing statistics and the internal > queue statistics (read/write merges).
Surely you can time the actual amount of time the I/O takes? It doesn't account for the virtio round-trip, but does it matter?
Why is the merge count important for the host?
> > The idea behind providing all of the stats on the stats vq (which is > basically what you see in '/dev/block/[device]/stats') is to give a > consistent snapshot of the state of the device. > >
What can you do with it?
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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