Re: [Qemu-devel] [PATCH RFC v2 0/4] block/qapi: refactor and optimize the qmp_query_blockstats()

[Fam Zheng <famz@redhat.com>]

On Mon, 12/19 15:02, Stefan Hajnoczi wrote:
> On Mon, Dec 19, 2016 at 04:51:22PM +0800, Dou Liyang wrote:
> > These patches aim to refactor the qmp_query_blockstats() and
> > improve the performance by reducing the running time of it.
> > 
> > qmp_query_blockstats() is used to monitor the blockstats, it
> > querys all the graph_bdrv_states or monitor_block_backends.
> > 
> > There are the two jobs:
> > 
> > 1 For the performance:
> > 
> > 1.1 the time it takes(ns) in each time:
> > the disk numbers     | 10    | 500
> > -------------------------------------
> > before these patches | 19429 | 667722 
> > after these patches  | 17516 | 557044
> > 
> > 1.2 the I/O performance is degraded(%) during the monitor:
> > 
> > the disk numbers     | 10    | 500
> > -------------------------------------
> > before these patches | 1.3   | 14.2
> > after these patches  | 0.8   | 9.1
> 
> Do you know what is consuming the remaining 9.1%?
> 
> I'm surprised to see such a high performance impact caused by a QMP
> command.

If it's "performance is 9.1% worse only during the 557044 ns when the QMP
command is being processed", it's probably becaues the main loop is stalled a
bit, and it's not a big problem. I'd be very surprised if the degradation is
more longer than that.

Fam

> 
> Please post your QEMU command-line.