David Xu wrote:
On Wednesday 10 May 2006 02:23, Kris Kennaway wrote:
There are at least several issues here:
...This may be general issues like
gettimeofday() on Linux vs FreeBSD; clearly there is something *very
big* to blame here. Mysql does do *lots* of such calls ...
My last recall is that gettimeofday is not a syscall on Linux...
I recall Matt talking about implementing gettimeofday()
without a syscall. The basic idea is to have the kernel
record some constants in a page that's mapped across
all processes, then libc can just read the time from
a known location.
It might be nice to combine this with some of the
other ideas being tossed around here:
* On each clock tick, store a base time in
a known location (page mapped read-only, no-execute
across all memory maps)
* libc can just read the base time (accurate
to the clock rate) from a constant. Very, very fast.
* For higher resolution, the kernel could record
TSC and CPU clock speed data (per-CPU? Hmmm...)
and libc could use that to fine-tune the time?
Still some details I need to think through...
Tim
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