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On Thu, Jun 30, 2005 at 06:17:26PM +0200, Ingo Molnar wrote: > > * Paul E. McKenney <paulmck@us.ibm.com> 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 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/ | |||||||||
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