Messages in this thread | | | Date | Tue, 17 Dec 2002 11:11:19 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Intel P6 vs P7 system call performance |
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dean gaudet wrote: > On Mon, 16 Dec 2002, Linus Torvalds wrote: > >>It's not as good as a pure user-mode solution using tsc could be, but >>we've seen the kinds of complexities that has with multi-CPU systems, and >>they are so painful that I suspect the sysenter approach is a lot more >>palatable even if it doesn't allow for the absolute best theoretical >>numbers. > > don't many of the multi-CPU problems with tsc go away because you've got a > per-cpu physical page for the vsyscall? > > i.e. per-cpu tsc epoch and scaling can be set on that page. > > the only trouble i know of is what happens when an interrupt occurs and > the task is rescheduled on another cpu... in theory you could test %eip > against 0xfffffxxx and "rollback" (or complete) any incomplete > gettimeofday call prior to saving a task's state. but i bet that test is > undesirable on all interrupt paths. >
Exactly. This is a real problem.
-hpa
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