Messages in this thread | | | Date | Mon, 22 Sep 2008 13:28:17 -0700 | From | "john stultz" <> | Subject | Re: printing current system time from kernel space |
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On Sun, Sep 21, 2008 at 10:18 PM, George Nychis <gnychis@cmu.edu> wrote: > I am looking to measure the latency of USB data between kernel space and > user space. The user space driver uses a URB to get data from the device to > the kernel and finally to user space. > > To measure this latency, I was thinking of printing the current system time > when a read occurs/succeeds in drivers/usb/core/devio.c at the function > usbdev_read(), and then again in user space when the URB succeeds in > reading. Then, I could subtract the two times to get the latency. > > I spent some time googling, but could not find out how or if it is possible > to read the current system time in kernel space. I could insert a printk() > somewhere in usbdev_read() then. > > If it is not possible to read the current system time, is there some other > shared clock between kernel and user space that I could use for this?
Kernel: getnstimeofday() Userland: clock_gettime(CLOCK_MONOTONIC, ...)
Those two should give you the same data. So printing timespecs from kernel space that come from getnstimeofday() and comparing it to userland clock_gettime(CLOCK_MONOTONIC,...) hopefully will give you what you want.
Let me know if I misunderstood.
thanks -john
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