On Wed, Feb 24, 2010 at 02:12:47PM +0800, Wu Fengguang wrote: > On Wed, Feb 24, 2010 at 01:22:15PM +0800, Dave Chinner wrote: > > What I'm trying to say is that while I agree with your premise that > > a 7.8MB readahead window is probably far larger than was ever > > intended, I disagree with your methodology and environment for > > selecting a better default value. The default readahead value needs > > to work well in as many situations as possible, not just in perfect > > 1:1 client/server environment. > > Good points. It's imprudent to change a default value based on one > single benchmark. Need to collect more data, which may take time.. Agreed - better to spend time now to get it right... > > > It sounds silly to have > > > > > > client_readahead_size > server_readahead_size > > > > I don't think it is - the client readahead has to take into account > > the network latency as well as the server latency. e.g. a network > > with a high bandwidth but high latency is going to need much more > > client side readahead than a high bandwidth, low latency network to > > get the same throughput. Hence it is not uncommon to see larger > > readahead windows on network clients than for local disk access. > > Hmm I wonder if I can simulate a high-bandwidth high-latency network > with e1000's RxIntDelay/TxIntDelay parameters.. I think netem is the blessed method of emulating different network behaviours. There's a howto+faq for setting it up here: http://www.linuxfoundation.org/collaborate/workgroups/networking/netem Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>