We had found during performance measurement/analysis that with 2 cpus and napi disabled, and the system transmitting (tcp), the cpus get too busy due to receive interrupt handling, reducing performance by around 10%. But then again, when the number of cpus increase, the interrupt scaling is much better and msi-x gives better numbers.
We are modifying the driver to enable napi with msi-x, but this work is in progress and may get released in a few months. The Xframe hardware has 8 independent dma channels for transmit and receive, with doorbells for each channel. Multiple channels are in use for a single netdev. In one of the variations of this driver that is not released to netdev, the received packets are steered to a channel based on hashing on a preconfigured criteria such as sockets on tcp_ipv4, udp_ipv4, tcp_ipv6, udp_ipv6 or addresses in ipv4/6. The transmits are handled in a similar manner. The current napi implementation looks like - driver_poll(struct net_device *dev, int *budget) where as, something like - driver_poll(struct context *context, int *budget) would be ideal for hardware like ours. Each channel could schedule a respective poller, rather than the current method which requires synchronization between the poller and the channels. Ram > -----Original Message----- > From: Jeff Garzik [mailto:[EMAIL PROTECTED] > Sent: Friday, August 10, 2007 10:39 AM > To: Rick Jones > Cc: Sivakumar Subramani; netdev@vger.kernel.org; support > Subject: Re: [PATCH 2.6.24]S2io: Default to IntA interrupt type when there > are less than 4 CPUs in the system. > > Rick Jones wrote: > > Sivakumar Subramani wrote: > >> - Default to IntA interrupt type when there are less than 4 CPUs in > >> the system. > > > > It might be good to include _why_ in the comment(s). I certainly am > > curious to know the reason, and it would be good to have in there for > > "posterity" should the underlying conditions change. > > Indeed. I really want to know 'why'? > > Jeff > > - 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
