On Tue, 2013-11-26 at 09:52 +0100, Peter Zijlstra wrote: > On Tue, Nov 26, 2013 at 12:12:31AM -0800, Davidlohr Bueso wrote: > > > I am becoming hesitant about this approach. The following are some > > results, from my quad-core laptop, measuring the latency of nthread > > wakeups (1 at a time). In addition, failed wait calls never occur -- so > > we don't end up including the (otherwise minimal) overhead of the list > > queue+dequeue, only measuring the smp_mb() usage when !empty list never > > occurs. > > > > +---------+--------------------+--------+-------------------+--------+----------+ > > | threads | baseline time (ms) | stddev | patched time (ms) | stddev | > > overhead | > > +---------+--------------------+--------+-------------------+--------+----------+ > > | 512 | 4.2410 | 0.9762 | 12.3660 | 5.1020 | > > +191.58% | > > | 256 | 2.7750 | 0.3997 | 7.0220 | 2.9436 | > > +153.04% | > > | 128 | 1.4910 | 0.4188 | 3.7430 | 0.8223 | > > +151.03% | > > | 64 | 0.8970 | 0.3455 | 2.5570 | 0.3710 | > > +185.06% | > > | 32 | 0.3620 | 0.2242 | 1.1300 | 0.4716 | > > +212.15% | > > +---------+--------------------+--------+-------------------+--------+----------+ > > > > Whee, this is far more overhead than I would have expected... pretty > impressive really for a simple mfence ;-)
*sigh* I just realized I had some extra debugging options in the .config I ran for the patched kernel. This probably explains why the huge overhead. I'll rerun and report shortly. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
