On Mon, 15 Oct 2007 14:40:25 +0200 Daniel Schaffrath <[EMAIL PROTECTED]> wrote:
> On 2007/10/02 , at 18:47, Stephen Hemminger wrote: > > > On Tue, 2 Oct 2007 09:25:34 -0700 > > [EMAIL PROTECTED] (Larry McVoy) wrote: > > > >>> If the server side is the source of the data, i.e, it's transfer > >>> is a > >>> write loop, then I get the bad behaviour. > >>> ... > >>> So is this a bug or intentional? > >> > >> For whatever it is worth, I believed that we used to get better > >> performance > >> from the same hardware. My guess is that it changed somewhere > >> between > >> 2.6.15-1-k7 and 2.6.18-5-k7. > > > > For the period from 2.6.15 to 2.6.18, the kernel by default enabled > > TCP > > Appropriate Byte Counting. This caused bad performance on > > applications that > > did small writes. > Stephen, maybe you can provide me with some specifics here? > > Thanks a lot!! > Daniel > Read the RFC3465 for explanation of TCP ABC. What happens is that applications that do multiple small writes will end up using up their window. Typically these applications are not streaming enough data to grow the congestion window so they get held after 4 writes until an ACK comes back. The fix for the application (which also helps on all OS's and TCP versions as well) is to use a call like writev() or sendmsg() to aggregate the small header blocks together into a single send. -- Stephen Hemminger <[EMAIL PROTECTED]> - 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
