go back to 256 requests per queue

From:	 Andrew Morton <akpm@zip.com.au>
To:	 Linus Torvalds <torvalds@transmeta.com>
Subject: [patch 8/19] go back to 256 requests per queue
Date:	 Sun, 16 Jun 2002 23:52:15 -0700
Cc:	 lkml <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@suse.de>



The request queue was increased from 256 slots to 512 in 2.5.20.  The
throughput of `dbench 128' on Randy's 384 megabyte machine fell 40%.

We do need to understand why that happened, and what we can learn from
it.  But in the meanwhile I'd suggest that we go back to 256 slots so
that this known problem doesn't impact people's evaluation and tuning
of 2.5 performance.



--- 2.5.22/drivers/block/ll_rw_blk.c~256-requests	Sun Jun 16 22:50:18 2002
+++ 2.5.22-akpm/drivers/block/ll_rw_blk.c	Sun Jun 16 23:22:46 2002
@@ -2002,8 +2002,8 @@ int __init blk_dev_init(void)
 	queue_nr_requests = (total_ram >> 8) & ~15;	/* One per quarter-megabyte */
 	if (queue_nr_requests < 32)
 		queue_nr_requests = 32;
-	if (queue_nr_requests > 512)
-		queue_nr_requests = 512;
+	if (queue_nr_requests > 256)
+		queue_nr_requests = 256;
 
 	/*
 	 * Batch frees according to queue length

-
-
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