Re: nanosleep() for shorted than schedule slice

[christos%astron.com@localhost (Christos Zoulas)]

In article <1n8j63y.1pcs0owrn6gceM%manu%netbsd.org@localhost>,
Emmanuel Dreyfus <manu%netbsd.org@localhost> wrote:
>Hello
>
>I just encountered a situation where PHP performance on NetBSD is rather
>weak compared to Linux or MacOS X.
>
>The code calls PHP's uniqid() a lot of time. uniqid() creates an unique
>id based on the clock. In order to avoid giving the same value for two
>consecutive calls, PHP's uniqid() calls usleep(1) to skip to make sure
>the current microsecond has changed.
>
>On NetBSD this turns into a 16 ms sleep, which is 16000 what was
>requested. This happens because the kernel scheduled another process,
>which is the behavior documented in the man page. However the result is
>that a PHP script full of uniqid() is ridiculously slow. 
>
>I worked around the problem by reimplementing PHP uniqid() using
>uuidgen(), but that kind of performance problem could exist in many
>other softwares.
>
>I wonder if it would make sense for nanosleep(2) to check that requested
>sleeping time is shorter than a schedule slice, and if it is, spin the
>CPU instead of scheduling another process. Any opinion on this?

The solution is to implement "tickless kernel". It is not that difficult.

christos