Xserver and Gettimeofday

[Gabor Gombas]

On Wed, Aug 29, 2007 at 09:07:47PM -0700, Keith Packard wrote:

> It actually takes a timer signal every 20ms instead of calling
> gettimeofday for this purpose. Unfortunately, we also have many spin
> loops that wait for the hardware to finish some operation, and those
> generally want to timeout when the hardware locks up. Those call
> gettimeofday repeatedly, and while it looks bad on a profile, it's
> really just spinning through the kernel rather than sitting solely in
> user space spinning.

E.g. Linux on AMD64 implements time() and gettimeofday() completely in
user-space (the kernel exports the time in the VDSO page that is mapped
into the address space of every process), while clock_gettime() is a
real syscall.

Gabor

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     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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