With a USB 2.0 webcam attached to the OTG port on an OMAP3 (applies to
overo gumstix, beagleboard, probably others) we see a high CPU load in a
kworker thread.
Between 2.6.33 and 2.6.34 musb_core.c changed.
IRQ handlers changed with the result that a worker in musb_core.c got
scheduled far more frequently than needed.
I've included a patch below against 3.7, but i think it'll apply against
mainline.
[I apologize for any whitespace mangling. I've also attached the patch.]
I'd like more eyeballs to tell me if this is right. I'd also like to
know who I need to talk to to get this pushed into mainline.
--Adam
# The MUSB IRQ schedules work on every interrupt.
# This is unnecessary, and causes excessive CPU load.
#
# Here we only schedule work if there is something for
# the worker to do.
Index: git/drivers/usb/musb/musb_core.c
===================================================================
--- git.orig/drivers/usb/musb/musb_core.c
+++ git/drivers/usb/musb/musb_core.c
@@ -925,7 +925,9 @@ b_host:
}
#endif
- schedule_work(&musb->irq_work);
+ if (musb->xceiv->state != musb->xceiv_old_state) {
+ schedule_work(&musb->irq_work);
+ }
return handled;
}
# The MUSB IRQ schedules work on every interrupt.
# This is unnecessary, and causes excessive CPU load.
#
# Here we only schedule work if there is something for
# the worker to do.
Index: git/drivers/usb/musb/musb_core.c
===================================================================
--- git.orig/drivers/usb/musb/musb_core.c
+++ git/drivers/usb/musb/musb_core.c
@@ -925,7 +925,9 @@ b_host:
}
#endif
- schedule_work(&musb->irq_work);
+ if (musb->xceiv->state != musb->xceiv_old_state) {
+ schedule_work(&musb->irq_work);
+ }
return handled;
}
