Messages in this thread | | | Date | Mon, 6 Oct 2008 14:18:29 +1100 | From | Dave Chinner <> | Subject | Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority |
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On Sat, Oct 04, 2008 at 05:45:00PM +1000, Aaron Carroll wrote: > Dave Chinner wrote: >> On Thu, Oct 02, 2008 at 05:32:04PM +0200, Bodo Eggert wrote: >>> Sounds like you need a priority class besides sync and async. >> >> There's BIO_META now as well, which I was testing at the same time >> as RT priority. Marking all the metadata I/O as BIO_META did help, >> but once again I never got to determining if that was a result of >> the different tagging or the priority increase. > > What exactly do you want META to mean? Strict prioritisation over > all other non-META requests, or just more frequent and/or larger > dispatches? Should META requests be sorted?
The real question is "what was it supposed to mean"? AFAICT, it was added to a couple of filesystems to be used to tag superblock read I/O. Why - I don't know - there's a distinct lack of documentation surrounding these bio flags. :/
Realistically, I'm not sure that having a separate queue for BIO_META will buy us anything, given that noop is quite often the fastest scheduler for XFS because it enables interleaved metadata I/O to be merged with data I/O. Like I said, I was not able to spend the time to determine exactly how BIO_META affected I/O patterns, so I can't really comment on whether it is really necessary or not.
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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