Messages in this thread | | | Date | Mon, 10 Feb 2003 05:51:07 +0100 | From | Jakob Oestergaard <> | Subject | Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest] |
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On Sun, Feb 09, 2003 at 08:33:43PM -0800, Andrew Morton wrote: > David Lang <david.lang@digitalinsight.com> wrote: > > > > note that issuing a fsync should change all pending writes to 'syncronous' > > as should writes to any partition mounted with the sync option, or writes > > to a directory with the S flag set. > > We know, at I/O submission time, whether a write is to be waited upon. > That's in writeback_control.sync_mode. > > That, combined with an assumption that "all reads are synchronous" would > allow the outgoing BIOs to be appropriately tagged.
This may be a terribly stupid question, if so pls. just tell me :)
I assume read-ahead requests go elsewhere? Or do we assume that someone is waiting for them as well?
If we assume they are synchronous, that would be rather unfair especially on multi-user systems - and the 90% accuracy that Rik suggested would seem exaggerated to say the least (accuracy would be more like 10% on a good day).
> It's still approximate. An exact solution would involve only marking I/O as > synchronous when some process actually waits on its completion. I do not > believe that all the extra lookup and locking infrastructure and storage > which this would require is justified. Certainly not in a first iteration.
Just a quirk; NFS file servers.
The client does read-ahead - the nfsd on the server-side will wait for the read request, thus the read is synchronous... But it's not.
-- ................................................................ : jakob@unthought.net : And I see the elder races, : :.........................: putrid forms of man : : Jakob Østergaard : See him rise and claim the earth, : : OZ9ABN : his downfall is at hand. : :.........................:............{Konkhra}...............: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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