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Date: Fri, 07 Sep 2007 10:38:15 +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 Hi Mandeep, Mandeep Singh Baines wrote: > Hi James, > > I like the idea of staying in poll longer. > > My comments are similar to what Jamal and Stephen have already said. > > A tunable (via sysfs) would be nice. > > A timer might be preferred to jiffy polling. Jiffy polling will not increase > latency the way a timer would. However, jiffy polling will consume a lot more > CPU than a timer would. Hence more power. For jiffy polling, you could have > thousands of calls to poll for a single packet received. While in a timer > approach the numbers of polls per packet is upper bound to 2. Why would using a timer to hold off the napi_complete() rather than jiffy count limit the polls per packet to 2? > I think it may difficult to make poll efficient for the no packet case because, > at a minimum, you have to poll the device state via the has_work method. Why wouldn't it be efficient? It would usually be done by reading an "interrupt pending" register. > If you go to a timer implementation then having a tunable will be important. > Different appications will have different requirements on delay and jitter. > Some applications may want to trade delay/jitter for less CPU/power > consumption and some may not. I agree. I'm leaning towards a new ethtool parameter to control this to be consistent with other per-device tunables. > imho, the work should definately be pursued further:) Thanks Mandeep. I'll try. :) -- 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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