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Date: Sat, 26 Jan 2008 18:11:46 +0100 From: Tomasz Chmielewski <mangoo@...g.org> To: toralf.foerster@....de Cc: LKML <linux-kernel@...r.kernel.org> Subject: Re: (ondemand) CPU governor regression between 2.6.23 and 2.6.24 Toralf Förster wrote: > I use a 1-liner for a simple performance check : "time factor 819734028463158891" > Here is the result for the new (Gentoo) kernel 2.6.24: > > With the ondemand governor of the I get: > > tfoerste@n22 ~/tmp $ time factor 819734028463158891 > 819734028463158891: 3 273244676154386297 > > real 0m32.997s > user 0m15.732s > sys 0m0.014s > > With the ondemand governor the CPU runs at 600 MHz, > whereas with the performance governor I get : > > tfoerste@n22 ~/tmp $ time factor 819734028463158891 > 819734028463158891: 3 273244676154386297 > > real 0m10.893s > user 0m5.444s > sys 0m0.000s > > (~5.5 sec as I expected) b/c the CPU is set to 1.7 GHz. > > The ondeman governor of previous kernel versions however automatically increased > the CPU speed from 600 MHz to 1.7 GHz. > > My system is a ThinkPad T41, I'll attach the .config During the test, run top, and watch your CPU usage. Does it go above 80% (the default for /sys/devices/system/cpu/cpu0/cpufreq/ondemand/up_threshold). ondemand CPUfreq governor has a few tunables, described in Documentation/cpu-freq. One of them is up_threshold: up_threshold: defines what the average CPU usaged between the samplings of 'sampling_rate' needs to be for the kernel to make a decision on whether it should increase the frequency. For example when it is set to its default value of '80' it means that between the checking intervals the CPU needs to be on average more than 80% in use to then decide that the CPU frequency needs to be increased. What CPUFreq processor driver are you using? I had a similar problem with CPUfreq and dm-crypt (slow reads), see (more setup problem than something kernel-related): http://blog.wpkg.org/2008/01/22/cpufreq-and-dm-crypt-performance-problems/ -- Tomasz Chmielewski -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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