On Thu, Jun 30, 2005 at 06:17:26PM +0200, Ingo Molnar wrote:
>
> * Paul E. McKenney <[email protected]> wrote:
>
> > > another point is that this test is measuring the overhead of PREEMPT_RT,
> > > without measuring the benefit of the cost: RT-task scheduling latencies.
> > > We know since the rtirq patch (to which i-pipe is quite similar) that we
> > > can achieve good irq-service latencies via relatively simple means, but
> > > that's not what PREEMPT_RT attempts to do. (PREEMPT_RT necessarily has
> > > to have good irq-response times too, but much of the focus went to the
> > > other aspects of RT task scheduling.)
> >
> > Agreed, a PREEMPT_RT-to-IPIPE comparison will never be an
> > apples-to-apples comparison. Raw data will never be a substitute for
> > careful thought, right? ;-)
>
> well, it could still be tested, since it's so easy: the dohell script is
> already doing all of that as it runs rtc_wakeup - which runs a
> SCHED_FIFO task and carefully measures wakeup latencies. If it is used
> with 1024 Hz (the default) and it can be used in every test without
> impacting the system load in any noticeable way.
OK, I think that I finally understand what you are getting at -- and I
agree that it would be interesting to get latency measurements during the
actual lmbench runs. However, if I understand correctly, you would want
roughly 1,000,000 latency measurements per lmbench run segment, which,
at 1024 Hz, would mean that each segment would take about 20 minutes.
A single lmbench run would then take many hours.
Is this really what you are getting at, or are you instead thinking
in terms of a single maximum-latency measurement covering the entire
lmbench run?
Thanx, Paul
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |