Re: [PATCH] sched_clock: Provide local_clock() and improve documentation

[Chad Talbott]

On Fri, May 28, 2010 at 6:13 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> + * local_clock()      -- is cpu_clock() on the current cpu.

Pretty sure this should read, "is cpu_clock() on *some* cpu," since
there is no guarantee in a preemptible kernel that local_clock()
returns on the same CPU that it was called from. The caller has to do
the preempt protection itself.

The function could be written as follows (thanks Salman Qazi):

u64 local_clock(unsigned int *where)
{
       u64 clock;
       unsigned long flags;

       local_irq_save(flags);
       *where = smp_processor_id();
       clock = sched_clock_cpu(*where);
       local_irq_restore(flags);

       return clock;
}

but I don't see the utility of the resulting routine.

Chad
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