I am not clear with delay loop.May be some of you can help here. http://lxr.linux.no/#linux+v2.6.33/init/calibrate.c#L54 In comments it is mentioning So, we do * 1. pre_start <- When we are sure that jiffy switch hasn't happened * 2. check jiffy switch * 3. start <- timer value before or after jiffy switch * 4. post_start <- When we are sure that jiffy switch has happened What is all that pre_start and why is it needed to be used over here? Here is some thing which I am wondering not because of logic in same program What is the CPU busy with between timer ticks I guess it is the calculation of delay as mentioned here in this code and what exactly is meant by timer tick? If you can see the following comment on the above mentioned link it says A simple loop like .........wont do I am not clear why they mentioned a simple loop wont do ? /* 045 * A simple loop like 046 * while ( jiffies < start_jiffies+1) 047 * start = read_current_timer(); 048 * will not do. As we don't really know whether jiffy switch 049 * happened first or timer_value was read first. And some asynchronous 050 * event can happen between these two events introducing errors in lpj. 051 * 052 * So, we do -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
