On Monday 27 August 2007 17:51, James Chapman wrote: > In the second half of my previous reply (which seems to have been > deleted), I suggest a way to avoid this problem without using hardware > interrupt mitigation / coalescing. Original text is quoted below. > > >> I've seen the same and I'm suggesting that the NAPI driver keeps > >> itself in polled mode for N polls or M jiffies after it sees > >> workdone=0. This has always worked for me in packet forwarding > >> scenarios to maximize packets/sec and minimize latency. > > To implement this, there's no need for timers, hrtimers or generic NAPI > support that others have suggested. A driver's poll() would set an > internal flag and record the current jiffies value when finding > workdone=0 rather than doing an immediate napi_complete(). Early in > poll() it would test this flag and if set, do a low-cost test to see if > it had any work to do. If no work, it would check the saved jiffies > value and do the napi_complete() only if no work has been done for a > configurable number of jiffies. This keeps interrupts disabled longer at > the expense of many more calls to poll() where no work is done. So > critical to this scheme is modifying the driver's poll() to fastpath the > case of having no work to do while waiting for its local jiffy count to > expire. >
The problem I see with this approach is that the time that passes between two jiffies might be too long for 10G ethernet adapters. (I tried to implement a timer based approach with usual timers and the result was a disaster). HW interrupts / or HP timer avoid the jiffy problem as they activate softIRQs as soon as you call netif_rx_schedule. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
