Re: [PATCH] RTC: Add mmap method to rtc character driver

H. Peter Anvin
2006-07-25T21:08:15Z

Jim Gettys wrote:
>
> Some of us want/need both tickless and smart scheduling in the X server.
>
> To give a bit of data: on my machine, a 1x1 rectangle can go almost 2
> million rectangles/second; a 500x500 rectangle is only 2800/second. You
> can see the tremendous variation (and this is on accelerated hardware;
> the variation can in fact be much larger than this, if the operation has
> to be done in software fall-backs).
>
> This is why the X server needs to know the time so much, so cheaply; we
> have to be able to tell how much time a given client has been using, and
> it can't be computed from anything but the time; otherwise individual
> clients can "starve" other clients, and interactive feel goes to pot.
> - Jim
>

That's why I'm suggesting adding a cheap, possibly low-res, gettimeofday
virtual system call in case there is no way for the kernel to provide
userspace with a cheap full-resolution gettimeofday. Obviously, if a
high-quality gettimeofday is available, then they can be linked together
by the kernel.

-hpa