Re: 2.4.1pre8 slowdown on dbench tests

[Andrea Arcangeli <andrea@suse.de>]

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.

Marcelo can you give a try with `high_queued_sectors = total_ram / 3' and
low_queued_sectors = high_queued_sectors / 2 and drop the big ram machine
check?

Andrea
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