Hi David,
Jivin Bou lays it down ...
Hi all,
sorry for posting this again (I hope whoever could comment on the
original post "just lost it" :) ).
I would appreciate anyone's thoughts on this.
Don't recall seeing it, but then that doesn't mean a lot ;-)
Hi all,
On a "normal" kernel (no special tuning), kernel space tasks have more
priority than userspace ones? Is that correct?
Not as far as I know, unless a kernel task increases it's priority
I think it is the same, of course it can do whatever it likes, you
would have to check.
I think that apart from normal priorities (using nice), there are some
more priorities in the kernel (other than SCHED_NORMAL)
Here is what I am experiencing and trying to find a solution.
I have an IXP425 based board, running madwifi for the Atheros cards,
acting as a wifi router. I also use userspace programs (boa http server
and cgi apps) to configure it.
When the board is on heavy load (Wireless stations connected to the
board and pass lots of traffic), my web apps run extremely slow. Even
the serial console responds that slow.
This is most likely due to interrupt load and "at interrupt time"
processing. That is higher priority than processes.
Yes, this seems to be my problem.
Is there a solution to this? Would CONFIG_PREEMPT help at all? Or for
something like this you have to use a RT kernel?
NAPI can help, there are many drivers in the kernel that implement it
and you may be able to apply the same techniques to whatever drivers are
causing your latencies.
This was GREAT info. NAPI did help a lot. Well, it is not that fast, but
response time is acceptable.
Many many thanks!!!
P.S. I did not see any difference changing the weight (packets that
could be processed at once) of the poll function.
Cheers,
Bou
Assuming that the user space application can have a specific pid, is
there any "patch" that can be applied to the kernel's scheduler to give
it some more priority?
I cannot tell if this slow down occurs to kernel versus user space
priorities, or to the bunch of interrupts per second.
You want to look into kernel profiling (profile and oprofile).
Cheers,
Davidm
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