Re: [Qemu-devel] [PATCH] qemu-img: Add cache command line option

[Kevin Wolf]

Am 16.06.2011 16:43, schrieb Kevin Wolf:
> Am 16.06.2011 16:28, schrieb Christoph Hellwig:
>> On Wed, Jun 15, 2011 at 09:46:10AM -0400, Federico Simoncelli wrote:
>>> qemu-img currently writes disk images using writeback and filling
>>> up the cache buffers which are then flushed by the kernel preventing
>>> other processes from accessing the storage.
>>> This is particularly bad in cluster environments where time-based
>>> algorithms might be in place and accessing the storage within
>>> certain timeouts is critical.
>>> This patch adds the option to choose a cache method when writing
>>> disk images.
>>
>> Allowing to chose the mode is of course fine, but what about also
>> choosing a good default?  writethrough doesn't really make any sense
>> for qemu-img, given that we can trivially flush the cache at the end
>> of the operations.  I'd also say that using the buffer cache doesn't
>> make sense either, as there is little point in caching these operations.
> 
> Right, we need to keep the defaults as they are. That is, for convert
> unsafe and for everything else writeback. The patch seems to make
> writeback the default for everything.

Federico, are you going to fix this in a v4?

Kevin