Messages in this thread | | | Date | Fri, 19 Jan 2001 02:46:10 +0100 | From | Andi Kleen <> | Subject | Re: 2.4.1pre8 slowdown on dbench tests |
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On Fri, Jan 19, 2001 at 02:40:23AM +0100, Jens Axboe wrote: > On Fri, Jan 19 2001, Andrea Arcangeli wrote: > > On Thu, Jan 18, 2001 at 03:17:13PM -0200, Marcelo Tosatti wrote: > > > Jens, can be the -blk patch the reason for the slowdown I'm seeing? > > > > This heuristic is way too aggressive: > > > > /* > > * Try to keep 128MB max hysteris. If not possible, > > * use half of RAM > > */ > > high_queued_sectors = (total_ram * 2) / 3; > > low_queued_sectors = high_queued_sectors - MB(128); > > if (low_queued_sectors < 0) > > low_queued_sectors = total_ram / 2; > > > > /* > > * for big RAM machines (>= 384MB), use more for I/O > > */ > > if (total_ram >= MB(384)) { > > high_queued_sectors = (total_ram * 4) / 5; > > low_queued_sectors = high_queued_sectors - MB(128); > > } > > > > 2/3 of ram locked down in the I/O queue is way too much. 1/3 should be > > ok. big RAM machines needs way less than 1/3 locked down. > > Yes I agree, that values should probably be tweaked a bit. I'll > try and squeeze some testing in to generate the best possible > values.
Please also add a sysctl. I always feel uncomfortable with such hardcoded heuristics. There tends to be always another workload where the heuristic fails and manual tuning is useful.
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