lkml.org 
[lkml]   [2004]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Jackit-devel] Re: Statistical methods for latency profiling

On Sun, 1 Aug 2004, Lee Revell wrote:

> So stressing the filesystem moves the center to the right a bit, from
> 6-7 to 9-10, and *drastically* lengthens the 'tail'.

basically each codepath has a typical latency distribution, and when a
workload uses multiple codepaths then the latencies get intermixed almost
linearly.

> These numbers suggest to me that a lot of the latencies from 47 usecs
> and up are caused by one code path, because they are so uniformly
> distributed over the upper part of the histogram. The prime suspect of
> course being the ide io completions. I tested this theory by lowering
> max_sectors_kb from 64 to 32:

> These numbers all point to the ide sg completion code as the only thing
> on the system generating latencies over ~42 usecs.

yep, that's a fair assumption. Once the IO-APIC irq-redirection problems
are solved i'll try to further thread the IDE completion IRQ to remove
that ~100 usecs latency.

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

\
 
 \ /
  Last update: 2005-03-22 14:04    [W:0.765 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site