Monday, November 8, 2010

"We sometimes do this trick"

Recently on lkml we had a patch proposal by Don Zickus.

I had a minor nit, because I thought that it does make sense
to simplify this loop

       for_each_present_cpu(cpu) {
               if (per_cpu(watchdog_nmi_touch, cpu) != true)
                       per_cpu(watchdog_nmi_touch, cpu) = true;

       for_each_present_cpu(cpu) {
               per_cpu(watchdog_nmi_touch, cpu) = true;

Andrew Morton wrote in responce:
We sometimes do this trick to avoid dirtying lots of cachelines
which already held the correct value.  It'll be extra-benefical
when dealing with other CPU's data, I expect.

This is really reasonable. Once again, try to think in opposite
each time you make a decision.

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