Re: Assuming that TAS() will succeed the first time is verboten

On Fri, Dec 29, 2000 at 10:54:00AM -0800, Mikheev, Vadim wrote:
> > > The code is based on some odd assumptions. A select() with 0 delay
> > > returns immediately unless there is an interrupt during its
> > > (very short!) time in kernel space.
> >
> > Yeah, I've wondered whether the 0 entries in s_spincycle[]
> > shouldn't be 1. The code author evidently expected select()
> > to at least yield the processor even with delay 0, but the select()
> > man pages I have handy say that it will "return immediately" when delay
> > is 0.
>
> I've run some tests with 5 instead of 0 and afair performance was worse,
> so we should carefully test !0 values.

This is not surprising. Five microseconds is a long time, and the
current s_spincycle does it repeatedly.

> Actually, one slocks are held
> longer than anothers - probably we should use different delays...

I don't understand the last remark. Are you proposing to mix some
random numbers into the delays?

Did you try it with

#define S_NSPINCYCLE 2
int s_spincycle[S_NSPINCYCLE] = {1, 1000};

or even

#define S_NSPINCYCLE 1
int s_spincycle[S_NSPINCYCLE] = {1};

?

Nathan Myers
ncm(at)zembu(dot)com