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Re: [Qemu-devel] a suggestion to extend the query block stats commands f


From: Paolo Bonzini
Subject: Re: [Qemu-devel] a suggestion to extend the query block stats commands for multi-disk case
Date: Mon, 5 Dec 2016 12:57:21 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0


On 05/12/2016 12:53, Stefan Hajnoczi wrote:
> Adding the BlockBackend *query_blk parameter is a reasonable short-term
> workaround.  I wonder if the polling stats APIs need to be rethought in
> the longer term.
> 
> Regarding the low-level details of block statistics inside QEMU, we can
> probably collect statistics without requiring the AioContext lock.  This
> means guest I/O processing does not need to be interrupted.  There
> should be some RCU-style scheme that can be used to extract the stats.

The question is also what level of consistency you want.  Perhaps as
long as you can access it atomically (so no tearing of values) you don't
need a lock at all, blk_ref/unref is enough.

Paolo



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