Re: 2.4.1pre8 slowdown on dbench tests

[Jens Axboe <axboe@suse.de>]

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.

-- 
* Jens Axboe <axboe@suse.de>
* SuSE Labs
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