From 3467811e26660eb46bc655234573d22d6876d5f9 Mon Sep 17 00:00:00 2001
From: Steven Noonan <snoonan@amazon.com>
Date: Fri, 17 Feb 2012 12:04:44 -0800
Subject: [PATCH] xen-blkfront: make blkif_io_lock spinlock per-device

This patch moves the global blkif_io_lock to the per-device structure. The
spinlock seems to exists for two reasons: to disable IRQs when in the interrupt
handlers for blkfront, and to protect the blkfront VBDs when a detachment is
requested.

Having a global blkif_io_lock doesn't make sense given the use case, and it
drastically hinders performance due to contention. All VBDs with pending IOs
have to take the lock in order to get work done, which serializes everything
pretty badly.

Signed-off-by: Steven Noonan <snoonan@amazon.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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