Hi! On 14:40 Fri 28 Nov , yogeshwar sonawane wrote: > Hi all, > > 1) I have a driver code providing ioctl,read, write, mmap etc. entry points. > Now, i want to find the execution time of each entry point for comparison. > > How this can be done ? > for ex. > > take time_stamp1 > call entry point > take time_stamp2 > > The above code from a user application can measure the execution time > ? Timing functions in user space are close to the real time ? > > > 2) Which timing functions should be used to get the, close to correct > time, in user & kernel space ? > Mainly the purpose is to calculate timing interval. I would call the syscalls multiple times. This way, there is no requirement for a ultra high resolution clock. gettimeofday() will probably be enough. But there are some other pitfalls: - The time the ioctl, ... takes depends on whether the required things are already cached in the CPU cache or not. If you want to measure how long it takes with a cold cache, you can try to trash it between runs. But then you cannot easily call gettimeofday() before and after a loop of the ioctl(). You can call gettimeofday(), ioctl(), gettimeofday(), trash the cpu cache, then do it again. But - gettimeofday() itself takes some time. This means even if the resolution is high enough or if you average of a lot samples, this time always adds to the result. If you trash the CPU cache, you may also alter the time gettimeofday() takes. You may want to offset this by calling a gettimeofday() and ignoging the result to get the data into the cache. You can also try to offset the gettimeofday() times by measuring the time gettimeofday() takes and substracting this of the result. - Do not run any other process to make sure that the benchmark process does get the cpu. - Something else may come up. -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
