Re: future developments of usbnet
From: Alan Stern <hidden>
Date: 2011-05-12 14:37:28
On Thu, 12 May 2011, Oliver Neukum wrote:
Am Mittwoch, 11. Mai 2011, 19:47:27 schrieb David Miller:quoted
Basically once you take you interrupt, and disable device interrupts, the generic net device layer calls your ->poll() routing with a "weight" You should not process more RX packets than this value. If you have less than "weight" work to do, you should do a napi_complete(), which takes you out of the polling group, and re-enable device interrupts. So the idea is that you keep getting ->poll()'d until there is no more RX work to do. The "weight" argument implements fairness amongst competing, actively polling, devices on the same CPU.Thank you, this is very informative. Our problem here is that USB doesn't work sanely without interrupts. We can stop IO regarding rx, but we cannot stop interrupts if we want to do rx.
The idea behind NAPI can be adapted to the usbnet context. The basic idea is that the driver is allowed to accept only a limited number of packets, driven by polling from the NAPI core. Therefore usbnet's poll routine should take the "weight" argument as an indication of how many outstanding rx URBs are allowed. Each time the poll routine is called, it should check to see if any rx URBs have completed since the previous poll. If not then there is no network traffic, so usbnet can take itself out of the poll loop. Otherwise, the number of outstanding URBs should be adjusted (by unlinking some or submitting more -- subject to some fixed maximum limit) to match the new "weight". Does that make sense? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html