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Subject[PATCH] device model: Do a quickcheck for driver binding before doing an expensive check

From: Arjan van de Ven <>
Subject: [PATCH] device model: Do a quickcheck for driver binding before doing an expensive check

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

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 <>
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 */

Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,

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