Messages in this thread | | | Date | Tue, 5 Mar 2002 08:42:21 +0100 | From | Jens Axboe <> | Subject | Re: [PATCH] 2.4.x write barriers (updated for ext3) |
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On Mon, Mar 04 2002, Daniel Phillips wrote: > > writeback data order is important, mostly because of where the data blocks > > are in relation to the log. If you've got bdflush unloading data blocks > > to the disk, and another process doing a commit, the drive's queue > > might look like this: > > > > data1, data2, data3, commit1, data4, data5 etc. > > > > If commit1 is an ordered tag, the drive is required to flush > > data1, data2 and data3, then write the commit, then seek back > > for data4 and data5. > > > > If commit1 is not an ordered tag, the drive can write all the > > data blocks, then seek back to get the commit. > > We can have more than one queue per device I think. Then we can have reads > unaffected by write barriers, for example. It never makes sense for a the > write barrier to wait on a read.
No, there will always be at most one queue for a device. There might be more than one device on a queue, though, so yes the implementation at the block/queue level still leaves something to be desired.
-- Jens Axboe
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