On 12/16/14 09:04, Eric Blake wrote:
> Wire up backing chain recursion. Note that for now, we just use
> the same allocation numbers for read-only backing files as what
> offline domains would report. It is not the correct allocation
> number for qcow2 over block devices during block-commit, and it
> misses out on the fact that qemu also reports read statistics on
> backing files that are worth knowing about (seriously - for a
> thin-provisioned setup, it would be nice to easily get at a count
> of how many reads were serviced from the backing file in relation
> to reads serviced by the active layer). But it is at least
> sufficient to prove that the algorithm is working, and to let
> other people start coding to the interface while waiting for
> later patches that get the correct information.
>
> For a running domain, where one of the two images has a backing
> file, I see the traditional output:
>
> $ virsh domstats --block testvm2
> Domain: 'testvm2'
> block.count=2
> block.0.name=vda
> block.0.path=/tmp/wrapper.qcow2
> block.0.rd.reqs=1
> block.0.rd.bytes=512
> block.0.rd.times=28858
> block.0.wr.reqs=0
> block.0.wr.bytes=0
> block.0.wr.times=0
> block.0.fl.reqs=0
> block.0.fl.times=0
> block.0.allocation=0
> block.0.capacity=1310720000
> block.0.physical=200704
> block.1.name=vdb
> block.1.path=/dev/sda7
> block.1.rd.reqs=0
> block.1.rd.bytes=0
> block.1.rd.times=0
> block.1.wr.reqs=0
> block.1.wr.bytes=0
> block.1.wr.times=0
> block.1.fl.reqs=0
> block.1.fl.times=0
> block.1.allocation=0
> block.1.capacity=1310720000
>
> vs. the new output:
>
> $ virsh domstats --block --backing testvm2
> Domain: 'testvm2'
> block.count=3
> block.0.name=vda
> block.0.path=/tmp/wrapper.qcow2
> block.0.rd.reqs=1
> block.0.rd.bytes=512
> block.0.rd.times=28858
> block.0.wr.reqs=0
> block.0.wr.bytes=0
> block.0.wr.times=0
> block.0.fl.reqs=0
> block.0.fl.times=0
> block.0.allocation=0
> block.0.capacity=1310720000
> block.0.physical=200704
> block.1.name=vda
> block.1.path=/dev/sda6
> block.1.backingIndex=1
> block.1.allocation=1073741824
> block.1.capacity=1310720000
> block.1.physical=1073741824
> block.2.name=vdb
> block.2.path=/dev/sda7
> block.2.rd.reqs=0
> block.2.rd.bytes=0
> block.2.rd.times=0
> block.2.wr.reqs=0
> block.2.wr.bytes=0
> block.2.wr.times=0
> block.2.fl.reqs=0
> block.2.fl.times=0
> block.2.allocation=0
> block.2.capacity=1310720000
>
> * src/qemu/qemu_driver.c (QEMU_DOMAIN_STATS_BACKING): New internal
> enum bit.
> (qemuConnectGetAllDomainStats): Recognize new user flag, and pass
> details to...
> (qemuDomainGetStatsBlock): ...here, where we can do longer recursion.
> (qemuDomainGetStatsOneBlock): Output new field.
> * src/qemu/qemu_domain.c (qemuDomainStorageAlias): Tolerate NULL
> alias input for offline domain.
>
> Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
> ---
> src/qemu/qemu_domain.c | 3 +++
> src/qemu/qemu_driver.c | 57 +++++++++++++++++++++++++++++++++++++++-----------
> 2 files changed, 48 insertions(+), 12 deletions(-)
>
> @@ -18651,18 +18673,25 @@ qemuDomainGetStatsBlock(virQEMUDriverPtr driver,
>
> for (; i < dom->def->ndisks; i++) {
> virDomainDiskDefPtr disk = dom->def->disks[i];
> + virStorageSourcePtr src = disk->src;
> + unsigned int backing_idx = 0;
>
> - if (qemuDomainGetStatsOneBlock(driver, cfg, dom, record, maxparams,
> - disk, disk->src, i, abbreviated,
> - stats) < 0)
> - goto cleanup;
> + while (src && (!backing_idx || backing)) {
I'd make the special case of the first element a bit more obvious by
using "backing_idx == 0" rather than the negation sign used usually with
pointers.
> + if (qemuDomainGetStatsOneBlock(driver, cfg, dom, record, maxparams,
> + disk, src, visited, backing_idx,
> + abbreviated, stats) < 0)
> + goto cleanup;
> + visited++;
> + backing_idx++;
> + src = src->backingStore;
> + }
> }
>
> ret = 0;
As an additional thought. The stats are now extermely long for VMs with
a long backing chain and few of the stats tend to be 0 always. We could
start skipping them perhaps (at least for the non-top, devices)
ACK.
Peter
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