Hi, > I find something interesting; kernel has msleep, but it > doesn't have usleep. > Does that mean the minimum time kernel can react is msecond > instead of usecond? > so if users want to count useconds, they have to do the busy waiting, > execute some looping assembly instructions? You are roughly right. If you don't want to busy loop (udelay / mdelay), then you will have to sleep. The granularity of this sleep depends on how frequently the timer interrupt ticks (HZ). Thus if HZ is 1000, then you cannot sleep for a period less than 1 msec. > > If my consumption is correct, where I can find the evidence? > BTW, does Hz has anything related to kernel timing? > From the comment in the kernel, it says > Hz: clock ticks generated per second > Does that mean the kernel will get #Hz timer interrupts per second? Yes. > Whz the value of Hz is 100? if the minimum reaction time of kernel is > msecond, the value of Hz should be 1000, right? Default value of HZ depends on the architecture - and you can change it as well. If HZ is 100, then minimum sleep is 10 ms. If you call msleep(1), you will still sleep for 10 msec atleast - msleep() only guarantees that you will sleep for ATLEAST the time you specified - you may obviously sleep for longer. >> >> At bootup the kernel measures the delay loop speed of >> each CPU. CPU frequency scaling might make the loop > > would you please let me know where the source code is? > (measuring loop speed of cpu and scale cpu frequency) calibrate_delay() Thanks, Rajat -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
