From: Alan D. Brunelle <Alan.Brunelle@hp.com>
Date: Tue, 29 Apr 2008 12:44:19 +0000 (+0200)
Subject: block: Skip I/O merges when disabled
X-Git-Tag: v2.6.26-rc1~372^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ac9fafa1243640349aa481adf473db283a695766;p=pandora-kernel.git

block: Skip I/O merges when disabled

The block I/O + elevator + I/O scheduler code spend a lot of time trying
to merge I/Os -- rightfully so under "normal" circumstances. However,
if one were to know that the incoming I/O stream was /very/ random in
nature, the cycles are wasted.

This patch adds a per-request_queue tunable that (when set) disables
merge attempts (beyond the simple one-hit cache check), thus freeing up
a non-trivial amount of CPU cycles.

Signed-off-by: Alan D. Brunelle <alan.brunelle@hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---

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