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Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes |
Date: |
Mon, 20 Sep 2010 17:46:02 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100907 Fedora/3.0.7-1.fc12 Thunderbird/3.0.7 |
Am 20.09.2010 17:33, schrieb Avi Kivity:
> 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.
Oops, my bad. Swap 4 and 5, that's what I meant. We don't need a flush
after writing the L2 entry until we need to flush for other reasons.
Kevin
- [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Kevin Wolf, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Anthony Liguori, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Kevin Wolf, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Anthony Liguori, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Kevin Wolf, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Anthony Liguori, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Anthony Liguori, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Avi Kivity, 2010/09/20
- Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes, Kevin Wolf, 2010/09/21