Improving the kernel/i386 timecounter performance (GSoC
proposal)
Maxim Sobolev
sobomax at FreeBSD.org
Mon Mar 30 18:45:38 PDT 2009
Robert Watson wrote:
> Part of the point of mapping in the page at execve()-time, or
> fork()-time for per-process pages (which I'm not entirely convinced we
> need yet) is to avoid the cost of an extra device open, mmap, etc, for
> every execve(), which can be quite expensive. I stuck a prototype page
You don't really need to do it on every execve() unconditionally. It
could be done on demand in libc, so that only when thread pass certain
threshold, the "common page optimization code" kicks in and does its
open/mmap/etc magic. Otherwise, "normal" syscall is performed. The
implementation could be as simple as counter in the appropriate libc
routine, so that optimization engages after certain number of calls. For
syscalls that return time it's also easy to do frequency thresholds, so
that for example gettimeofday() only gets optimized if threads calls it
more frequently that 1 call/sec.
-Maxim
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