Re: [9fans] usb slowness

[erik quanstrom <quanstro@quanstro.net>]

On Mon Mar  5 11:06:43 EST 2012, 9fans@hamnavoe.com wrote:
> > if you could temporarly run a 9atom kernel,
> 
> With the normal kernel, you can use acid or db to look at the intrtimes
> array to see the spread of cpu times used in each interrupt vector entry.
> 
> See http://9fans.net/archive/2003/11/520

i didn't find the original histogram very useful.  it is not scaled
by the speed of the processor nor type of interrupt.  the slots
in the histogram are appropriate for 8259 interrupts on a 2000-era
processor (100µs increments).  almost all the interrupts i see are
< 20µs.  the 82598 on my relativly slow cpu server averages 2.5µs
per interrupt.

it's also a pain to print out without a file in addition to /dev/irqalloc.
i found the absolute count and absolute # of cpu cycles (to avoid
predivision sloppiness) to be a lot more useful for the general case.

a hisogram sure could be useful, but i think i'd want to taylor it to
a specific problem.  and i haven't had one yet.

- erik