Messages in this thread | | | Date | Fri, 26 Feb 1999 15:12:12 -0500 | From | Josip Loncaric <> | Subject | Re: Linux 2.2.2 TCP delays every 41st small packet by 10-20 ms |
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Andrea Arcangeli wrote: > > On Thu, 25 Feb 1999, Josip Loncaric wrote: > > >The conclusion is this: in Linux TCP, every N-th small packet is delayed > >by 1-2 "jiffies" (defined by the 100 Hz system clock). For Linux kernel > > This 1-2 jiffies made me thing again at the PSH thing. Probably I am > completly out but could you try this patch?
Your patch improved things by a factor of 20. The easiest way for me to explain how is to enclose a GIF file (<7KB, I hope this is not too much). This plots intermessage time in clock ticks (400 MHz clock), sorted from largest to smallest. Red dots are the unmodified Linux kernel 2.2.2; green dots are after Andrea's patch. Horizontal scales (message number after sorting by delay) are not directly comparable because a lot more messages could be sent after Andrea's patch, so the green curve is shifted to the right in this log-log plot.
Atypically large delays now cluster around 1 millisecond instead of 20 milliseconds. In both cases, a vast majority of the messages are spaced by less than 100 microseconds. Even after the patch, five delays of 200 milliseconds out of the 420,602 measured were seen, but this might be due to some unavoidable system activity during the test.
Sincerely, Josip
-- Dr. Josip Loncaric, Senior Staff Scientist mailto:josip@icase.edu ICASE, Mail Stop 403 http://www.icase.edu/~josip/ NASA Langley Research Center mailto:j.loncaric@larc.nasa.gov Hampton, VA 23681-2199, USA Tel. +1 757 864-2192 Fax +1 757 864-6134[image] | |