Messages in this thread |  | | Date | Tue, 6 Feb 2001 13:09:09 -0500 (EST) | From | Ben LaHaise <> | Subject | Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait |
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On Tue, 6 Feb 2001, Jens Axboe wrote:
> Stephen already covered this point, the merging is not a problem > to deal with for read-ahead. The underlying system can easily
I just wanted to make sure that was clear =)
> queue that in nice big chunks. Delayed allocation makes it > easier to to flush big chunks as well. I seem to recall the xfs people > having problems with the lack of merging causing a performance hit > on smaller I/O.
That's where readaround buffers come into play. If we have a fixed number of readaround buffers that are used when small ios are issued, they should provide a low overhead means of substantially improving things like find (which reads many nearby inodes out of order but sequentially). I need to implement this can get cache hit rates for various workloads. ;-)
> Of course merging doesn't have to happen in ll_rw_blk. > > > As for io completion, can't we just issue seperate requests for the > > critical data and the readahead? That way for SCSI disks, the important > > io should be finished while the readahead can continue. Thoughts? > > Priorities?
Definately. I'd like to be able to issue readaheads with a "don't bother executing if this request unless the cost is low" bit set. It might also be helpful for heavy multiuser loads (or even a single user with multiple processes) to ensure progress is made for others.
-ben
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