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Subject[PATCH 29/46] device model: Do a quickcheck for driver binding before doing an expensive check
Date
From: Arjan van de Ven <arjan@linux.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@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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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