Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes

[Avi Kivity]

 On 09/20/2010 05:33 PM, Avi Kivity wrote:
>  On 09/20/2010 05:08 PM, Kevin Wolf wrote:
> > >
> > >  Let's expand it a bit more:
> > >
> > >  1. Update refcount table
> > >  2. bdrv_flush
> > >  3. Update L2 entry
> > >  4. Write data to disk
> > >  5. Report write complete
> > >
> > >  I'm struggling to understand how a thread helps out.
> >
> > This sequence becomes:
> >
> > 1. Update refcount table
> > 2. Write data to disk
> > 3. Report write complete
> >
> > And only later:
> >
> > 4. Update L2 entry
> > 5. bdrv_flush (possibly merged with other flushes)
>
> The L2 update needs to happen after we're sure the refcount update is 
> stable, so need a bdrv_flush between them.
>
> Still, the basic idea looks sound.  You can do many refcount updates, 
> flush, many L2 updates, flush.


Oh, your original RFC has that flush in place, so all is good.

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