Timers and timing, was: MySQL Performance 6.0rc1
Robert Watson
rwatson at FreeBSD.org
Fri Oct 28 06:08:03 PDT 2005
On Fri, 28 Oct 2005, David Xu wrote:
> Poul-Henning Kamp wrote:
>> In message <4361FDBE.7000500 at freebsd.org>, David Xu writes:
>>
>> the correct way to optimize this would be to add a time(2) systemcall
>> which returns the value of the kernel global time_second.
>
> Can we make a page in kernel address space which is readable my user
> code? put the variable in the page, I know read an integer is atomic-op,
> needn't lock, so syscall is not needed.
This approach has a lot of merit, as we can also potentially export other
information there (such as kernel preferences for system call mechanisms).
On the other hand, a lower risk change might be to simply add a new CLOCK_
type for lower resolution, and have a timer synchronize a variable to the
system clock once every 1/10 of a second. This avoids having to muck with
VM layout, etc.
Robert N M Watson
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