linux-kernel - [PATCH 29/46] device model: Do a quickcheck for driver binding before doing an expensive check

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Date:	Thu, 16 Oct 2008 10:10:30 -0700
From:	Greg Kroah-Hartman <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH 29/46] device model: Do a quickcheck for driver binding before doing an expensive check

From: Arjan van de Ven <arjan@...ux.intel.com>

This patch adds a quick check for the driver<->device match before
taking the locks and doin gthe expensive checks. Taking the lock hurts
in asynchronous boot context where the device lock gets hit; one of the
init functions takes the lock and goes to do an expensive hardware init;
the other init functions walk the same PCI list and get stuck on the
lock as a result.

For the common case, we can know there's no chance whatsoever of a match
if the device isn't in the drivers ID table... so this patch does that
check as a best-effort-avoid-the-lock approach.

Bootcharts for before and after can be seen at
http://www.fenrus.org/before.svg
http://www.fenrus.org/after.svg

Note the long time "agp_ali_init" takes in the first graph; my laptop
doesn't even have an ALI chip in it!  (the bootgraphs look a bit
dissimilar, but that's the point, the first one has a bunch of arbitrary
delays in it that cause it to look very different)

This reduces my kernel boot time by about 20%

Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 drivers/base/dd.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 3ac443b..20febc0 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -257,6 +257,9 @@ static int __driver_attach(struct device *dev, void *data)
 	 * is an error.
 	 */

+	if (drv->bus->match && !drv->bus->match(dev, drv))
+		return 0;
+
 	if (dev->parent)	/* Needed for USB */
 		down(&dev->parent->sem);
 	down(&dev->sem);
-- 
1.6.0.2

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