Messages in this thread | | | Date | Fri, 24 May 2002 02:46:06 -0700 | From | William Lee Irwin III <> | Subject | Re: Poor read performance when sequential write presents |
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On Fri, May 24, 2002 at 02:26:48AM -0700, Andrew Morton wrote: > Oh absolutely. That's the reason why 2.4 is beating 2.5 at tiobench with > more than one thread. 2.5 is alternating fairly between threads and 2.4 > is not. So 2.4 seeks less.
In one sense or another some sort of graceful transition to unfair behavior could be considered a kind of thrashing control; how meaningful that is in the context of disk I/O is a question I can't answer directly, though. Do you have any comments on this potential strategic unfairness?
On Fri, May 24, 2002 at 02:26:48AM -0700, Andrew Morton wrote: > I've been testing this extensively on 2.5 + multipage BIO I/O and when you > increase readahead from 32 pages (two BIOs) to 64 pages (4 BIOs), 2.5 goes > from perfect to horrid - each threads grabs the disk head and performs many, > many megabytes of read before any other thread gets a share. Net effect is > that the tiobench numbers are great, but any operation which involves > reading disk has 30 or 60 second latencies. > Interestingly, it seems specific to IDE. SCSI behaves well. > I have tons of traces and debug code - I'll bug Jens about this in a week or > so.
What kinds of phenomena appear to be associated with IDE's latencies? I recall some comments from prior IDE maintainers on poor interactions between generic disk I/O layers and IDE drivers, particularly with respect to small transactions being given to the drivers to perform. Are these comments still relevant, or is this of a different nature?
Cheers, Bill - 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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