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

From: Avi Kivity
Subject: Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes
Date: Mon, 20 Sep 2010 17:33:35 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100907 Fedora/3.1.3-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.3

 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.

error compiling committee.c: too many arguments to function

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