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Date: Thu, 13 Dec 2007 00:54:45 +0100 (CET) From: Jan Engelhardt <jengelh@...putergmbh.de> To: Rene Herman <rene.herman@...il.com> cc: Linux Kernel <linux-kernel@...r.kernel.org>, dpreed@...d.com, Alan Cox <alan@...rguk.ukuu.org.uk>, pavel@....cz, andi@...stfloor.org, rol@...917.net, Krzysztof Halasa <khc@...waw.pl>, david@...idnewall.com, hpa@...or.com, john@...ffel.org, linux-os@...logic.com Subject: Re: [RFT] Port 0x80 I/O speed On Dec 12 2007 00:31, Rene Herman wrote: > > Would some people on x86 (both 32 and 64) be kind enough to compile and run the > attached program? This is about testing how long I/O port access to port 0x80 > takes. It measures in CPU cycles so CPU speed is crucial in reporting. > Transmeta TM5800 CPU with nominal frequency 933 MHz, but it has a hardware(!) 'ondemand' governor over the range of frequencies that the user allowed scaling over, irrespective of the software governor. (That is, if the CPU can do 300,533 and 933 MHz, and setting the min/max to 300/533 will cause the hardware to 'ondemand' between 300 and 533 only. And that even if 'performance' is set on the software side - so the only way to enforce 'performance' is to actually set min=933.) 00:46 takeshi:../cpu0/cpufreq # echo 300000 >scaling_min_freq 00:46 takeshi:../cpu0/cpufreq # echo 933000 >scaling_max_freq 00:42 takeshi:/dev/shm # for ((x=1;x<=10;++x)); do ./port80 ; done cycles: out 1514, in 584 cycles: out 1371, in 516 cycles: out 1291, in 472 cycles: out 1304, in 437 cycles: out 1308, in 410 cycles: out 1315, in 419 cycles: out 1315, in 419 cycles: out 1314, in 419 cycles: out 1315, in 420 cycles: out 1315, in 419 00:44 takeshi:/dev/shm # for ((x=1;x<=10;++x)); do ./port80 ; done cycles: out 1511, in 596 cycles: out 1373, in 517 cycles: out 1293, in 470 cycles: out 1294, in 424 cycles: out 1304, in 414 cycles: out 1315, in 420 cycles: out 1313, in 418 cycles: out 1313, in 418 cycles: out 1314, in 420 cycles: out 1314, in 419 Increasing x above 10 yields only 1313-1315 values, so nothing more to see. Note the values < 1313!! They only happen during scaling. (I think scaling is the most important sideexercise in this test, even on hardware which does not have hardware governors - e.g. your average Intel/AMD CPUs.) Single frequencies: 00:46 takeshi:../cpu0/cpufreq # echo 933000 >scaling_min_freq 00:46 takeshi:../cpu0/cpufreq # echo 933000 >scaling_max_freq 00:46 takeshi:../cpu0/cpufreq # for ((x=1;x<=10;++x)); do /dev/shm/port80 ; donecycles: out 1314, in 419 cycles: out 1315, in 420 cycles: out 1314, in 419 cycles: out 1312, in 417 cycles: out 1315, in 420 cycles: out 1314, in 419 cycles: out 1313, in 419 cycles: out 1313, in 419 cycles: out 1314, in 419 cycles: out 1312, in 418 00:47 takeshi:../cpu0/cpufreq # echo 533000 >scaling_min_freq 00:47 takeshi:../cpu0/cpufreq # echo 533000 >scaling_max_freq 00:49 takeshi:../cpu0/cpufreq # for ((x=1;x<=10;++x)); do /dev/shm/port80 ; donecycles: out 1372, in 508 cycles: out 1370, in 509 cycles: out 1372, in 515 cycles: out 1372, in 503 cycles: out 1372, in 503 cycles: out 1370, in 509 cycles: out 1368, in 513 cycles: out 1372, in 516 cycles: out 1372, in 504 cycles: out 1372, in 516 00:47 takeshi:../cpu0/cpufreq # echo 300000 >scaling_min_freq 00:47 takeshi:../cpu0/cpufreq # echo 300000 >scaling_max_freq 00:48 takeshi:../cpu0/cpufreq # for ((x=1;x<=10;++x)); do /dev/shm/port80 ; donecycles: out 1515, in 650 cycles: out 1516, in 649 cycles: out 1517, in 651 cycles: out 1513, in 645 cycles: out 1514, in 649 cycles: out 1516, in 644 cycles: out 1517, in 651 cycles: out 1516, in 644 cycles: out 1512, in 647 cycles: out 1514, in 649 -- 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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