Is there a problem in timeval_to_jiffies?

[Henry Margies]

Hallo.


I'm working on an arm based embedded device running kernel 2.6.9.
I asked this question also on the arm mailing list, but nobody
could answer me my questions there, so I will try here :)

I have some problems with itimers. For example, if I set up a
timer using a period of 20ms, the system needs 30ms to send the
signal. I figured out, that it needs always 10ms more than I
want.

The problem seems to be located in the timeval_to_jiffies()
function.

In function do_setitimer() the following calculation is done:

     i = timeval_to_jiffies(&value->it_interval);

... where i is the interval for my timer. The problem is, that
for it_interval = 0 seconds and 20000 microseconds, i = 3. But
shouldn't it be 2? It looks like, the problem is somewhere in
here (timeval_to_jiffies()):

      return (((u64)sec * SEC_CONVERSION) +
                (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
                 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >>
			SEC_JIFFIE_SC;

I don't understand all of the formula in detail. But for me, it
looks like the problem is in USEC_ROUND.

Any ideas?

Thx in advance,
Henry

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