[PATCH xserver 01/20] Remove non-smart scheduler. Don't require setitimer.

[Peter Harris]

On 2015-11-17 15:10, Adam Jackson wrote:
> On Wed, 2015-11-11 at 22:02 -0800, Keith Packard wrote:
>> This allows the server to call GetTimeInMillis() after each request is
>> processed to avoid needing setitimer. -dumbSched now turns off the
>> setitimer.
> 
> I'm not sure there are real systems we'd be protecting by not requiring
> setitimer.  But, at least on my Ivybridge, this only dings noop
> performance by like 1% when using -dumbSched.  Probably this would be
> worse on non-vdso setups, but anyone with both of those problems is
> already in pretty bad shape.

Data point:

I've got a Dell box (also Ivy Bridge) where calling GetTimeInMillis()
after each request dings noop performance by like 30% because the TSC is
unstable.

Performance would be fine on Fedora, where the server uses
CLOCK_MONOTONIC_COARSE, but Ubuntu's CLOCK_MONOTONIC_COARSE only has a
4ms resolution so it falls back to reading the HPET every time.

That said, this box is an outlier. Every other recent box I can put my
hands on has a fast GetTimeInMillis().

Peter Harris
-- 
               Open Text Connectivity Solutions Group
Peter Harris                    http://connectivity.opentext.com/
Research and Development        Phone: +1 905 762 6001
pharris at opentext.com            Toll Free: 1 877 359 4866