From: Philipp Reisner <philipp.reisner@linbit.com>
Date: Tue, 9 Nov 2010 12:59:41 +0000 (+0100)
Subject: drbd: Implemented side-stepping in drbd_res_begin_io()
X-Git-Tag: v2.6.39-rc1~37^2~97
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f91ab6282df251d28aa4ad1bd85194ebe0a0115b;p=pandora-kernel.git

drbd: Implemented side-stepping in drbd_res_begin_io()

Before:
  drbd_rs_begin_io() locked app-IO out of an RS extent, and
  waited then until all previous app-IO in that area finished.
  (But not only until the disk-IO was finished but until the
   barrier/epoch ack came in for that == round trip time latency ++)

After:
  As soon as a new app-IO waits wants to start new IO on that
  RS extent, drbd_rs_begin_io() steps aside (clearing the
  BME_NO_WRITES flag again). It retries after 100ms.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
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