On 08/18/2011 11:29 AM, Sasha Levin wrote: > On Thu, 2011-08-18 at 08:10 -0700, Avi Kivity wrote: >> 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? >> > > I assumed that the time the request spends in the virtio layer is > (somewhat) significant, specially since that this is something that adds > up over time. > > Merge count can be useful for several testing scenarios (I'll describe > the reasoning behind this patch below). > >>> >>> 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 was actually planning on submitting another patch that would add > something similar into virtio-net. My plan was to enable collecting > statistics regarding memory, network and disk usage in a simple manner > without accessing guests.
Why not just add an interface that lets you read files from a guest either via a guest agent (like qemu-ga) or a purpose built PV device? That would let you access the guest's full sysfs which seems to be quite a lot more useful long term than adding a bunch of specific interfaces. Regards, Anthony Liguori _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/virtualization
