Re: nanosleep() for shorted than schedule slice

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Jul 2,  1:16pm, Christos Zoulas wrote:
} In article <1n8j63y.1pcs0owrn6gceM%manu%netbsd.org@localhost>,
} Emmanuel Dreyfus <manu%netbsd.org@localhost> wrote:
} >
} >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.

     The other option would be to tell PHP not to be so dumb.  What
happens on other OSes?  I find it hard to believe that we're the
only ones that aren't tickless.

}-- End of excerpt from Christos Zoulas