On Mon, 3 Dec 2012, Carsten Emde wrote: > On 11/30/2012 11:31 PM, Frank Rowand wrote: > > On 11/30/12 07:46, Simon Falsig wrote: > > > [..] > > > Bonus-question: > > > - Additionally, I've tried running cyclictest alongside with all the > > > above, and it actually performs rather well, without any substantial > > > spikes. A strange thing is though, that the results are actually better > > > with load than without? (running with -t1 -p 80 -n -i 10000 -l 10000) > > > - Loaded: Min: 16, Avg: 41, Max: 177 > > > - No load: Min: 16, Avg: 97, Max: 263 > > > > If the system is less loaded, then the idle thread might be able to > > enter deeper levels of sleep. Deeper levels of sleep have larger > > latencies to exit. You would have to look at your processor specific > > values for exiting sleep states to see if this is sufficient to explain > > the difference. > If running a half-decent version of cyclictest, sleep states are generally > disabled while cyclictest is running. Please watch the line > # /dev/cpu_dma_latency set to 0us > which essentially documents this mechanism. Yes, the name of the variable > "cpu_dma_latency" is not obvious and cyclictest could do a better job by > writing > Wrote 0 to /dev/cpu_dma_latency and keeping the path open to prevent > all cores from entering any sleep state > but this is another story. Not sure what you mean here, doesn't it keep the path open? John> -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
