On Tuesday 28 August 2007 11:22, James Chapman wrote: > > So in this scheme what runs ->poll() to process incoming packets? > > The hrtimer? > > No, the regular NAPI networking core calls ->poll() as usual; no timers > are involved. This scheme simply delays the napi_complete() from the > driver so the device stays in the poll list longer. It means that its > ->poll() will be called when there is no work to do for 1-2 jiffies, > hence the optimization at the top of ->poll() to efficiently handle that > case. The device's ->poll() is called by the NAPI core until it has > continuously done no work for 1-2 jiffies, at which point it finally > does the netif_rx_complete() and re-enables its interrupts. > I'm not sure if I understand your approach correctly. This approach may reduce the number of interrupts, but it does so by blocking the CPU for up to 1 jiffy (that can be quite some time on some platforms). So no other application / tasklet / softIRQ type can do anything in between. The CPU utilization does not drop at all, and I thought that is one reason why we try to reduce the number of interrupts.
> If people feel that holding the device in the poll list for 1-2 jiffies > is too long (because there are too many wasted polls), a counter could > be used to to delay the netif_rx_complete() by N polls instead. N would > be a value depending on CPU speed. I use the jiffy sampling method > because it results in some natural randomization of the actual delay > depending on when the jiffy value was sampled in relation to the jiffy tick. > Waiting for N polls seems to make no sense if there are no further network adapters in that machine. It would take no time to call poll N times in a row when no new packets arrive. There is no real delay as the net_rx_action function will do nothing else between the poll calls. Please correct me if I'm wrong. Regards, Jan-Bernd _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
