Messages in this thread | | | Subject | Re: Intel P6 vs P7 system call performance | Date | Mon, 09 Dec 2002 07:40:22 -0800 | From | erich@uruk ... |
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Mike Hayward <hayward@loup.net> wrote:
> I have been benchmarking Pentium 4 boxes against my Pentium III laptop > with the exact same kernel and executables as well as custom compiled > kernels. The Pentium III has a much lower clock rate and I have > noticed that system call performance (and hence io performance) is up > to an order of magnitude higher on my Pentium III laptop. 1k block IO > reads/writes are anemic on the Pentium 4, for example, so I'm trying > to figure out why and thought someone might have an idea. > > Notice below that the System Call overhead is much higher on the > Pentium 4 even though the cpu runs more than twice the speed and the > system has DDRAM, a 400 Mhz FSB, etc. I even get pretty remarkable > syscall/io performance on my Pentium III laptop vs. an otherwise idle > dual Xeon. > > See how the performance is nearly opposite of what one would expect: ... > M-Pentium III 850Mhz Sys Call Rate 433741.8 > Pentium 4 2Ghz Sys Call Rate 233637.8 > Xeon x 2 2.4Ghz Sys Call Rate 207684.2 ...[other benchmark deleted]... > Any ideas? Not sure I want to upgrade to the P7 architecture if this > is right, since for me system calls are probably more important than > raw cpu computational power.
You're assuming that ALL operations in a P4 are linearly faster than a P-III. This is definitely not the case.
A P4 has a much longer pipeline (for a many cases, considerably longer than the diagrams imply) than the P-III, and in particular it has a much longer latency in handling mode transitions.
The results you got don't surprise me whatsoever. In fact the raw system call transition instructions are likely 5x slower on the P4.
-- Erich Stefan Boleyn <erich@uruk.org> http://www.uruk.org/ "Reality is truly stranger than fiction; Probably why fiction is so popular" - 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/
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