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Date: Mon, 25 Aug 2008 08:33:52 +0200 From: Peter Zijlstra <peterz@...radead.org> To: linux-kernel <linux-kernel@...r.kernel.org>, cpufreq@...r.kernel.org Cc: Ingo Molnar <mingo@...e.hu>, davej <davej@...emonkey.org.uk> Subject: [BUG] cpufreq: constant cpu_khz Hi, I noticed that my sched_clock() was slow on a number of machine, so I started looking at cpufreq. I inserted the following printk in the set_cyc2ns_scale() function, which is called from the cpufreq change notifier: diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 46af716..8dffd82 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -261,6 +263,9 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu) if (cpu_khz) *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz; + printk(KERN_DEBUG "set_cyc2ns_scale: %lu %lu %d\n", + *scale, cpu_khz, cpu); + sched_clock_idle_wakeup_event(0); local_irq_restore(flags); } And on my laptop: root@...py:~# dmesg | grep cyc2ns | tail -10 [ 91.378693] set_cyc2ns_scale: 854 1198980 0 [ 91.378713] set_cyc2ns_scale: 854 1198980 0 [ 110.548064] set_cyc2ns_scale: 854 1198980 0 [ 110.548106] set_cyc2ns_scale: 854 1198980 0 [ 110.756121] set_cyc2ns_scale: 854 1198980 0 [ 110.756135] set_cyc2ns_scale: 854 1198980 0 [ 440.812063] set_cyc2ns_scale: 854 1198980 0 [ 440.812106] set_cyc2ns_scale: 854 1198980 0 [ 441.593140] set_cyc2ns_scale: 854 1198980 0 [ 441.593159] set_cyc2ns_scale: 854 1198980 0 even though I'm sure there were some 800 <-> 1200 MHz changes there esp. as: root@...py:~# cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 11 model name : Intel(R) Pentium(R) III Mobile CPU 1200MHz stepping : 1 cpu MHz : 798.000 cache size : 512 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 2 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr sse up nopl bogomips : 1598.64 clflush size : 32 power management: On my opteron: [root@...eron ~]# dmesg | grep cyc2ns | tail -10 [ 0.000000] set_cyc2ns_scale: 427 2394004 0 [ 0.000000] set_cyc2ns_scale: 427 2394004 1 [ 14.784154] set_cyc2ns_scale: 427 2394004 0 [ 14.788342] set_cyc2ns_scale: 427 2394004 1 [ 14.792789] set_cyc2ns_scale: 427 2394004 0 [ 14.797028] set_cyc2ns_scale: 427 2394004 1 [ 15.841049] set_cyc2ns_scale: 427 2394004 0 [ 15.845250] set_cyc2ns_scale: 427 2394004 1 [ 15.849503] set_cyc2ns_scale: 427 2394004 0 [ 15.853785] set_cyc2ns_scale: 427 2394004 1 [root@...eron ~]# cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 67 model name : Dual-Core AMD Opteron(tm) Processor 1216 stepping : 2 cpu MHz : 1000.000 cache size : 1024 KB physical id : 0 siblings : 2 core id : 0 cpu cores : 2 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow rep_good nopl pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy bogomips : 1995.00 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: ts fid vid ttp tm stc processor : 1 vendor_id : AuthenticAMD cpu family : 15 model : 67 model name : Dual-Core AMD Opteron(tm) Processor 1216 stepping : 2 cpu MHz : 1000.000 cache size : 1024 KB physical id : 0 siblings : 2 core id : 1 cpu cores : 2 apicid : 1 initial apicid : 1 fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow rep_good nopl pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy bogomips : 1995.00 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: ts fid vid ttp tm stc -- 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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