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Re: [Qemu-devel] [PATCH v2] block: Switch to host monotonic clock for IO

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v2] block: Switch to host monotonic clock for IO throttling
Date: Mon, 23 Mar 2015 16:02:13 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 23/03/2015 16:00, Stefan Hajnoczi wrote:
> On Mon, Mar 23, 2015 at 2:49 PM, Paolo Bonzini <address@hidden> wrote:
>> On 23/03/2015 15:28, Stefan Hajnoczi wrote:
>>> I'd like to know what problems exactly this patch fixes.  The test
>>> case for throttling actually relies on the virtual clock so it can be
>>> stepped deterministically.  What other legitimate cases are there
>>> where throttling is used outside a running qemu-system process?
>> Alberto brought up block jobs.  It is debatable whether block jobs
>> should be stopped while the VM is.
> This patch is unrelated to block jobs.  Block jobs use their own
> ratelimiting mechanism and the realtime clock (not vm clock).

Block jobs are also influenced by throttling though, if their underlying
BDS is throttled.  For example, streaming works by doing reads on a BDS
that is also visible to the VM and might be throttled.  Same for
mirroring or active-layer commit.


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