Messages in this thread | | | Subject | Re: [Perfctr-devel] Re: Enabling RDPMC in user space by default | From | Lee Revell <> | Date | Tue, 29 Nov 2005 14:05:43 -0500 |
| |
On Tue, 2005-11-29 at 10:29 -0800, John Reiser wrote: > Andi Kleen wrote: > > I think it's also a useful convention - RDTSC is becomming more and more > > useless and you cannot expect user applications who just want to > > measure some cycles to rely on ever changing instable or non existing > > performance counter APIs. > > Users are even more unhappy with ever-changing ABIs -- such as the > kernel taking away RDTSC. > > RDTSC+perfctr [Pettersson] still is the fastest way for user-mode code > to count something that is highly correlated with both "billable" > CPU time and "code quality" for a fixed task. With a little care > RDTSC is close enough to monotonic that I find it very useful. > Please don't take away user-mode RDTSC. >
The kernel didn't take this away, the hardware vendors did. For years although it was risky on paper it was perfectly usable as a cheap high res timer. I agree that it's unfortunate.
Lee
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |