Messages in this thread | | | Date | Mon, 16 Dec 2002 22:09:33 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: Intel P6 vs P7 system call performance |
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On Mon, 16 Dec 2002, Linus Torvalds wrote: > > On my P4 machine, a "getppid()" is 641 cycles with sysenter/sysexit, and > something like 1761 cycles with the old "int 0x80/iret" approach. That's a > noticeable improvement, but I have to say that I'm a bit disappointed in > the P4 still, it shouldn't be even that much.
On a slightly more real system call (gettimeofday - which actually matters in real life) the difference is still visible, but less so - because the system call itself takes more of the time, and the kernel entry overhead is thus not as clear.
For gettimeofday(), the results on my P4 are:
sysenter: 1280.425844 cycles int/iret: 2415.698224 cycles 1135.272380 cycles diff factor 1.886637
ie sysenter makes that system call almost twice as fast.
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.
Linus
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