Am 29.06.2011 14:23, schrieb Anthony Liguori: > On 06/29/2011 07:16 AM, Kevin Wolf wrote: >> Am 29.06.2011 14:06, schrieb Anthony Liguori: >>> On 06/29/2011 06:59 AM, Kevin Wolf wrote: >>>> Hi, >>>> >>>> I think we have touched this topic before during some IRC discussions or >>>> somewhere deep in a mailing list thread, but I think it hasn't been >>>> discussed on the list. >>>> >>>> Our default cache mode of cache=writethrough is extremely conservative >>>> and provides absolute safety at the cost of performance, >>> >>> But for the most part, we track bare metal fairly well in terms of block >>> performance, no? >>> >>> Or are you really referring to qcow2 as a specific example? In the >>> past, we used a different default caching mode for qcow2. I think that >>> could be done again if there was a compelling reason. >> >> No, people are also complaining about bad performance with raw. Which >> isn't really surprising when you do a flush after each single write >> request. O_SYNC is really much more than is needed in the average case. > > Which file system on the host?
Honestly, I don't know. Usually the problem is resolved with setting a different cache option, so nobody bothers to ask for details. I'd guess that it's ext4 in most cases. > At any rate, I'm a big fan of making wce tunable in the guest and then I > think setting wce=1 is quite reasonable to do by default. Okay, I think that's a fair requirement. So let's plan to implement this in 0.16. Christoph, it looks like we're back to your WCE patches then. Do you still work on them? Kevin
