From: John Heffner <[EMAIL PROTECTED]> Date: Thu, 27 Sep 2007 22:26:02 -0400
> I think it really does help in case (4) with old NICs that don't do rx > checksumming. I'm not sure how many people really care about this > anymore, but probably some...? > > OTOH, it would be nice to get rid of sysctl_tcp_low_latency. I know most high end apps use poll() so won't sleep in recvmsg() directly, but occasisionally they will, and even those that have a poll() triggered recvmsg() will run the backlog and do prequeue if packets arrive while they are processing the existing receive packets which is quite common. So for any app that ends up doing a prequeue it's a win because there is the issue of scheduling and cpu usage charging. If the ACK's are coming out of the stack at the rate that the application can pull data out of the receive queue, and no faster, this will pace the sender to send precisely how fast the receiver can get onto the cpu depending upon load. Furthermore, prequeue puts the stack input processing work into user context, which means that the users will be charged more fairly for the work that is done for them. When packets get fully processed in softirq context, that's bad because this is cpu usage which doesn't get charged to the user, and for TCP input processing this cpu usage is non-trivial and is multiplied by packet count. - 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
