Re: [time] add support for CLOCK_THREAD_CPUTIME_ID and CLOCK_PROCESS_CPUTIME_ID

[Ulrich Drepper <drepper@redhat.com>]

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Christoph Lameter wrote:

> +int do_posix_clock_thread_gettime(struct timespec *tp)
> +{
> +	jiffies_to_timespec(get_jiffies_64()-current->start_time, tp);
> +	return 0;
> +}
> +
> +int do_posix_clock_process_gettime(struct timespec *tp)
> +{
> +	jiffies_to_timespec(get_jiffies_64()-current->group_leader->start_time, tp);
> +	return 0;
> +}
> +

This is pretty useless.  Why would you need kernel support for this, it
just measures realtime.

We have an implementation of the CPU time in glibc which can easily be
changed to support clocks of this precision if there are no usable
timestamp counters (which is what is currently used).

And all this is not really what was really meant by "CPU time" in the
POSIX spec.  We hijacked this symbol, maybe incorrectly so.  What is
really meant is how much time a process/thread actually _uses_ the CPU
(hence the name).  I.e., the information contained in struct rusage.

For this I would love to get kernel support and we hopefully have soon a
patch for this.

- --
? Ulrich Drepper ? Red Hat, Inc. ? 444 Castro St ? Mountain View, CA ?
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