In message <c21e92e20510280248g6b47a7c6t79cb07e53a7db118_at_mail.gmail.com>, Jiawe i Ye writes: Very typical numbers... >kern.timecounter.hardware: ACPI-fast -> TSC > getpid(): 0.94267 > gettimeofday(): 1.25332 So timekeeping "as such" takes no more than 310nsec and that includes a TSC read of unknown duration. I consider the 310 nsec acceptable, but if this is a really big problem for people, somebody is welcome to start looking at doing inline assembler code to speed it up >kern.timecounter.hardware: TSC -> ACPI-fast > getpid(): 0.94788 > gettimeofday(): 2.29598 ACPI-fast does an inl() which seems to take a microsecond longer than rdtsc(). One microsecond is disgusting considering that the hardware lives in the chipset and was meant to improve timekeeping performance. >kern.timecounter.hardware: ACPI-fast -> i8254 > getpid(): 0.96921 > gettimeofday(): 5.01292 And i8254 does a outb() and several 8 bit inb on a simulated ISA bus and therefore takes 3.75 usec longer than rdtsc(). -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk_at_FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.Received on Fri Oct 28 2005 - 08:14:50 UTC
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