Re: [Qemu-devel] qcow2x

[Frediano Ziglio]

2011/8/2 Kevin Wolf <address@hidden>:
> Am 02.08.2011 17:29, schrieb Frediano Ziglio:
>>>> - L2 allocation can be done with relative data (this is not easy to do
>>>> with current code)
>>>
>>> What do you mean by that?
>>>
>>
>> Let's take an example. By allocation I mean give a position to
>> data/l2/refcount_table. Usually you cannot update/write L2 before data
>> is allocated and written if you don't want to get a L2 entry pointing
>> to garbage or unwritten data (if physically you write to a sector you
>> get new data or old one on fail, not data changing to anything else).
>> The exception to this is when even L2 table is not allocated. In this
>> case you can write L2 table with data cause in case of failure this
>> new L2 table is just not attached to anything (cause L1 still point to
>> old L2 or is not allocated). My patch can collapse these two cluster
>> writes in a single one. The key point of the patch is mainly
>> collapsing all writes as you can not blocking other writes if not
>> needed.
>
> Ok, I see.
>
> Not sure if it makes any measurable difference. With 64k clusters, an L2
> allocation happens only every 512 MB. But if it's not much code to
> support it, it's probably a good thing.
>

Let's see :)

I published a repo at gitorious. https://gitorious.org/qemu (yes, qemu
was free for me :) )

Currently there are 2 branches, qcow2x and my_cleanup. I think gitk
interface is much better. From my_cleanup branch from "qcow: allocate
QCowAIOCB structure using stack" to "qcow: embed qcow_aio_read_cb into
qcow_co_readv and qcow_aio_write_cb into qcow_co_writev" there are
cleanups for qcow while from "qcow2: removed unused fields" to "qcow2:
remove memory leak" there are cleanups for qcow2.

... omissis ...

>
> Works for me. Just anything that I can pull from.
>
>>> Are you in the #qemu IRC channel? I think we should coordinate our qcow2
>>> work a bit in order to avoid conflicting or duplicate work.
>>
>> No, I don't use irc that much (time shift problems and also connection
>> too). When are you online?
>
> Usually until something like 18:00 CEST (16:00 UTC).
>
> Kevin
>

:( me from 18:00 CEST

Frediano