Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb()

David Howells
2008-11-07T23:29:22Z

Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:

> Yes. Do you think the synchronization of the cycles counters is
> _perfect_ across CPUs so that there is no possible way whatsoever that
> two cycle counter values appear to go backward between CPUs ? (also
> taking in account delays in __m_cnt_hi write-back...)

Given there's currently only one CPU allowed, yes, I think it's perfect:-)

It's something to re-evaluate should Panasonic decide to do SMP.

> If we expect the only correct use-case to be with readl(), I don't see
> the problem with added synchronization.

It might be expensive if you don't actually want to call readl(). But that's
on a par with using funky instructions to read the TSC, I guess.

David