lkml.org 
[lkml]   [1999]   [Feb]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Linux 2.2.2 TCP delays every 41st small packet by 10-20 ms
Donald Becker wrote:
>
> On Fri, 26 Feb 1999, Josip Loncaric wrote:
>
> > Subject: Re: Linux 2.2.2 TCP delays every 41st small packet by 10-20 ms
> > 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
> ...
> > 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.
>
> Could you please try the following?
> Bump the RX_RING_SIZE and TX_RING_SIZE in the driver up to 128 or 256
> entries each. With enough memory this should have trivial free memory
> impact and remove any queue-limit noise in the measurments.
>
> This should have no significant average performance impact.
> If it does, there is something unexpected going on.

Increasing both ring sizes to 256 had no significant impact for most
messages, but the number of messages spaced by 200 milliseconds shot up
to 30. Prior to this test, the machines were rebooted and I believe
that they were completely dedicated to this test, so I have no
explanation for the 200 ms delays that were seen. I'll repeat the test
using a crossover cable, but this made no difference in previous tests.
With larger ring buffers, 70 messages were spaced by more than 1 ms, and
Andrea's patch did did not help much in those cases. BTW, this test
measured 414,374 intermessage delays.

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

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:50    [W:0.048 / U:0.548 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site