On Thursday 22 April 2010 11:22:20 pm Saravana Kannan wrote: > Dave, Venkatesh and other maintainers, > > Any comments? >From adjust_jiffies in cpufreq.c: * adjust_jiffies - adjust the system "loops_per_jiffy" * * This function alters the system "loops_per_jiffy" for the clock * speed change. Note that loops_per_jiffy cannot be updated on SMP * systems as each CPU might be scaled differently. So, use the arch * per-CPU loops_per_jiffy value wherever possible. For SMP case adjust_jiffies is just empty. udelay on x86 uses the per cpu loops_per_jiffy: cpu_data(raw_smp_processor_id()).loops_per_jiffy which does not get adjusted via adjust_jiffies() For me it looks as udelay is always wrong and sleeps too long on lower frequencies, but I may oversee something. It shouldn't be that hard to test this with a tiny test module which is measuring real udelay sleep times via tsc reads on a x86 machine with stable tsc. Doing that in a loop, print out the diff to how long it should have slept and doing that under lowered freq or whatever bad circumstances, should show worst cases after some time. Thomas -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
