Dave Jones wrote: ... > > But yes, for this to be even remotely feasible, there has to be a negligable > performance cost associated with it, which right now, we clearly don't have. > Given that the number of people running 4096 CPU boxes even in a few years time > will still be tiny, punishing the common case is obviously absurd. > > Dave > I did do some fairly extensive benchmarking between configs of NR_CPUS = 128 and 4096 and most performance hits were in the neighborhood of < 5% on systems with 8 cpus and 4GB of memory (our most common test system). [But changing cpumask_t's to be pointers instead of values will likely increase this.] I've tried to be very sensitive to this issue with all my previous changes, so convincing the distros to set NR_CPUS=4096 would be as painless for them as possible. ;-) Btw, huge count cpu systems I don't think are that far away. I believe the nextgen Larabbee chips will be geared towards HPC applications [instead of just GFX apps], and putting 4 of these chips on a motherboard would add up to 512 cpu threads (1024 if they support hyperthreading.) Thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
