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

Jim Gettys
2006-07-25T20:58:20Z

On Tue, 2006-07-25 at 16:47 -0400, Neil Horman wrote:

> >
> > The i386 vdso right now has only two entry points, as far as I can
> tell:
> > system call and signal return.
> >
> > There is no reason it couldn't have more than that. A
> low-resolution
> > and a high-resolution gettimeofday might be a good idea.
> >
> > -hpa
>
> Agreed. How about we take the /dev/rtc patch now (since its an added
> feature
> that doesn't hurt anything if its not used, as far as tickless kernels
> go), and
> I'll start working on doing gettimeofday in vdso for arches other than
> x86_64.
> That will give the X guys what they wanted until such time until all
> the other
> arches have a gettimeofday alternative that doesn't require kernel
> traps.
>

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

--
Jim Gettys
One Laptop Per Child