Re: Low capped TCP network speeds over the Internet

[mlelstv%serpens.de@localhost (Michael van Elst)]

gdt%lexort.com@localhost (Greg Troxel) writes:

>Looking at your file, it appears there is sudden massive packet loss,
>and there is fast retransmit, but the loss is beyond what fast
>retransmit can repair.

My current assumption is that packets get lost due to kernel locking.


>There is a TCP feature called "pacing" that attempts to spread out
>transmissions, but I am really unclear on whether it exists in deployed
>code.   My guess is no, not really.

We cannot do any kind of fine-grained pacing unless there would be
hardware support as we lack hires timers.

Most of our code writes packets to the interface send queue and the
transmitter gets (re-)armed by an interrupt. At high packet rates
that causes packet bursts, more if the hardware uses a large number
of send descriptors and more with deferred interrupts.

At some point, pacing needs to be supported by the hardware.