On 30/11/16 13:11 +0100, Sven Kieske wrote:
On 30/11/16 09:13, Yaniv Kaul wrote:
Thanks, but it really makes no sense to me. The direct IO by the VMs is going to a different storage than what the host is writing to, in most cases. The host would write to the local disk, the VMs - to a shared storage, across NFS or block layer or so. Moreover, their IO is not buffered. There is very little IO coming from the host itself, generally (I hope so!).
Partially unrelated - the trend today is actually to put NOOP on the VMs - the deadline is quite meaningless, as the host scheduler will reschedule anyway as it see fits. Most likely it is also a deadline scheduler (but could be NOOP as well if it's an all flash array, for example). Therefore there is no reason for anything but simple NOOP on the VMs themselves.
In short, I think it's an outdated decision that perhaps should be revisited. Not urgent, though. Y.
I know it's not the most cared about usecase but I'd like to add that this might affect local storage domains, which I happen to use a lot, and maybe others too.
Current values seem to be optimal; considering this use case I'd definitely leave it in place.
-- Mit freundlichen Grüßen / Regards
Sven Kieske
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