On Mon, Aug 19, 2013 at 07:04:18PM +0800, Ming Lei wrote: > Because usb_hcd_submit_urb is in the hotest path of usb core, > so use percpu counter to count URB instead of using atomic variable > because atomic operations are much slower than percpu operations. > > Cc: Oliver Neukum <oliver@xxxxxxxxxx> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx> > --- > drivers/usb/core/hcd.c | 4 ++-- > drivers/usb/core/sysfs.c | 7 ++++++- > drivers/usb/core/usb.c | 9 ++++++++- > drivers/usb/core/usb.h | 1 + > include/linux/usb.h | 2 +- > 5 files changed, 18 insertions(+), 5 deletions(-) And this really speeds things up? Exactly what does it? And it's not that atomic operations are "slower", it's just that the barriers involved can be slower, depending on what else is happening. If you look, you are already hitting atomic variables in the same path, so how can this change speed anything up? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
