On Tue, 10 Jun 2003, David S. Miller wrote: > Unfortunately, NAPI won't help him with the current way the 3c59x > driver works. It needs to provide a way to use MEM I/O before NAPI > would start to be of use to him. I don't really want to sound like defending the 3c59x driver, but... The 3c90x driver released by 3Com uses some mechanism "similar" to NAPI which is based on the on-board timer; these timer interrupts are scheduled dynamically. With this driver I would typically get TCP bandwidth figures 4-5 Mbps lower than those obtained with 3c59x and noticable difference in the parallel jobs timing (using MPI over TCP). I'm not saying that NAPI will perform the same way, just that there might be also hardware limits somewhere... But the real question is: does it make sense to spend time now in trying to improve a driver with hope for only a marginal speed increase ? After using these cards and the 3c59x driver with very good results for the past 4 years, I'm looking for GigE replacements. Shouldn't anybody concerned with performance do the same ? Does it make sense to pair a very fast CPU and memory with a 33MHz-32bit PCI bus ? And another important question: how much improvement can be gained from the driver ? Folks that do parallel computation over TCP over Ethernet know very well that the software in the kernel is the bottleneck (extra copies, TCP, IRQ management, etc). Packages that throw away TCP and use another communication protocol can typically achieve much better ping-pong times (they do have some other problems though) which shows that the hardware and NIC driver are capable enough. So until I see a profile showing that the CPU is spending most of the time in the driver, I won't be convinced that these changes are needed.... -- Bogdan Costescu IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868 E-mail: Bogdan.Costescu@IWR.Uni-Heidelberg.De - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
