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Date: Mon, 10 Sep 2007 10:33:34 +0100 From: James Chapman <jchapman@...alix.com> To: Mandeep Singh Baines <mandeep.baines@...il.com> CC: netdev@...r.kernel.org, hadi@...erus.ca, davem@...emloft.net, jeff@...zik.org, ossthema@...ibm.com, Stephen Hemminger <shemminger@...l.org> Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates Mandeep Singh Baines wrote: >> Why would using a timer to hold off the napi_complete() rather than >> jiffy count limit the polls per packet to 2? >> > I was thinking a timer could be used in the way suggested in Jamal's > paper. The driver would do nothing (park) until the timer expires. So > there would be no calls to poll for the duration of the timer. Hence, > this approach would add extra latency not present in a jiffy polling > approach. Ah, ok. I wasn't planning to test timer-driven polling. :) >> Why wouldn't it be efficient? It would usually be done by reading an >> "interrupt pending" register. >> > Reading the "interrupt pending" register would require an MMIO read. > MMIO reads are very expensive. In some systems the latency of an MMIO > read can be 1000x that of an L1 cache access. Agreed. Testing for any work being available should be as efficient as possible and would be driver specific. -- James Chapman Katalix Systems Ltd http://www.katalix.com Catalysts for your Embedded Linux software development - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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