[ltt-dev] sys time

[michel.dagenais@polymtl.ca (Michel Dagenais)]

On Fri, 2008-10-17 at 18:40 +0200, Gian Lorenzo Meocci wrote:
> I agree with you but this don't resolv my problem. Infact my problem
> is that "time" give me 1.74 sec of sys time when analising lttng-trace
> I obtain only 0.87.

The time command can be pretty far off when a process is making a lot of
system calls. It usually underestimates the user time, which is
consistent with what you are seeing. Basically, the kernel simply counts
a full jiffy for the process currently executing when the timer
generates an interrupt. If a process makes a lot of system calls, it
will often be scheduled at the beginning of a timer interval but will
quickly yield to another process and not be there at the timer
interrupt.