From SRS0+de3def591acb43d0ac0c+1848+infradead.org+arjan@casper.srs.infradead.org Mon Sep 15 10:04:14 2008 From: Arjan van de Ven Date: Sun, 14 Sep 2008 08:32:06 -0700 Subject: device model: Do a quickcheck for driver binding before doing an expensive check To: linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Cc: greg@kroah.com Message-ID: <20080914083206.0f42b2a7@infradead.org> From: Arjan van de Ven 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 Cc: Alan Stern Signed-off-by: Greg Kroah-Hartman --- drivers/base/dd.c | 3 +++ 1 file changed, 3 insertions(+) --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -257,6 +257,9 @@ static int __driver_attach(struct device * 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);