Re: [Qemu-block] I/O accounting overhaul

[Alberto Garcia]

On Wed 03 Jun 2015 04:18:45 PM CEST, Eric Blake wrote:

>> The accounting stats are stored in the BlockDriverState, but they're
>> actually from the device backed by the BDS, so they could probably be
>> moved there. For the interface we could extend BlockDeviceStats and
>> add the new fields, but query-blockstats works on BDS, so maybe we
>> need new API?
>
> We want stats per BDS (it would be nice to know how many reads are
> satisfied from the active layer, vs. how many are satisfied from the
> backing image, to know how stable and useful the backing image is).
> But we also want stats per BB (how many reads did the guest attempt,
> regardless of which BDS served the read).  So any good solution needs
> to work from both views (whether by two API, or by one with a flag, is
> bike-shedding).

That's right. As I said my priority is the stats from the BB (i.e. what
the guest can see), but I agree that any solution has to consider that
we want to have both eventually.

Berto