lkml.org 
[lkml]   [2008]   [Nov]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes
Ingo Molnar wrote:
> * Alexander van Heukelum <heukelum@fastmail.fm> wrote:
>
> hackbench is _way_ too noisy to measure such cycle-level differences
> as irq entry changes cause. It also does not really stress interrupts
> - it only stresses networking, the VFS and the scheduler.
>
> a better test might have been to generate a ton of interrupts, but
> even then it's _very_ hard to measure it properly. The best method is
> what i've suggested to you early on: run a loop in user-space and
> observe irq costs via RDTSC, as they happen. Then build a histogram
> and compare the before/after histogram. Compare best-case results as
> well (the first slot of the histogram), as those are statistically
> much more significant than a noisy average.
>

For what it's worth, I tested this out, and I'm pretty sure you need to
run a uniprocessor configuration (or system) for it to make sense --
otherwise you end up missing too many of the interrupts. I first tested
this on an 8-processor system and, well, came up with nothing.

I'm going to try this later on a uniprocessor, unless Alexander beats me
to it.

-hpa


\
 
 \ /
  Last update: 2008-11-10 16:43    [W:0.224 / U:0.984 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site