* Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote: > On Wed, 2011-06-15 at 12:11 -0700, Linus Torvalds wrote: > > > > > And it results in real problems. For example, if you use "perf record" > > to see what the hell is up, the use of kernel threads for RCU > > callbacks means that the RCU cost is never even seen. I don't know how > > Tim did his profiling to figure out the costs, and I don't know how he > > decided that the spinlock to semaphore conversion was the culprit, but > > it is entirely possible that Tim didn't actually bisect the problem, > > but instead used "perf record" on the exim task, saw that the > > semaphore costs had gone up, and decided that it must be the > > conversion. > > > > Yes, I was using perf to do the profiling. I thought that the mutex > conversion was the most likely culprit based on the change in > profile. have you used callgraph profiling (perf record -g) or flat profiling? Flat profiling can be misleading when there's proxy work done. Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>