On Thursday 02 February 2006 02:53, Greg Banks wrote: > On Thu, 2006-02-02 at 08:11, David S. Miller wrote: > > Van is not against NAPI, in fact he's taking NAPI to the next level. > > Softirq handling is overhead, and as this work shows, it is totally > > unnecessary overhead. > > I got the impression that his code was dynamically changing the > e1000 interrupt mitigation registers in response to load, in > other words using the capabilities of the hardware in a way that > NAPI deliberately avoids doing.
There was already talk some time ago to make NAPI drivers use the hardware mitigation again. The reason is when you have a workload that runs below overload and doesn't quite fill the queues and is a bit bursty, then NAPI tends to turn on/off the NIC interrupts quite often. At least on some chipsets (Tigon3 in particular) this seems to cause slowdowns compared to non NAPI. The idea (from Jamal originally iirc) was to use the hardware mitigation to cycle less often from polling to non polling state. Don't think it was ever implemented though. In the end we just eat the slowdown in that particular load. > > How in the world can you not understand how incredible this is? > > Maybe "you had to be there". Van's presentation was amazingly > convincing in person, in a way the slides don't convey. I've > not seen a standing ovation at a technical talk before ;-) Wish I had made it then. Perhaps I would see the light then @) > I'm very interested in vj channels for improving CPU usage of > NFS and Samba servers. However, after a few days to reflect, > I'm curious as to how the tx is improved. Yes i was missing that too. He hinted about getting rid of hard_start_xmit somehow, but then never touched it again. -Andi - 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
