Re: [Lse-tech] scalability of signal delivery for Posix Threads

[Ray Bryant]

Andi Kleen wrote:
> On Mon, Nov 22, 2004 at 05:51:59PM +0100, Andreas Schwab wrote:
>
> > Andi Kleen <ak@xxxxxxx> writes:
> >
> >
> > > At least in traditional signal semantics you have to call sigaction
> > > or signal in each signal handler to reset the signal. So that 
> > > assumption is not necessarily true.
> >
> > If you use sigaction then you get POSIX semantics, which don't have this
> > problem.
>
>
> It's just a common case where Ray's assumption is not true.
>
> -Andi

True enough.  And in that case the design that I was describing wouldn't
make sigaction() that much more expensive since if you are not in the POSIX
thread environment (more precisely, the thread was not created with
CLONE_SIGHAND) each thread has its own sighand structure and the "global" 
locking mechanisum I had proposed would only require the taking of one 
additional lock.

However, special casing ITIMER_PROF is also a reasonable avenue of approach.
The performance monitor code can also deliver signals to user space when
a sampling buffer overflows, and this can have the same kind of scaling
problem as ITIMER_PROF.  I'll have to do a little research to figure out
how exactly that works, but that signal (SIGIO?) would also be a candidate
for special casing on our platform.

--
Best Regards,
Ray
-----------------------------------------------
                  Ray Bryant
512-453-9679 (work)         512-507-7807 (cell)
raybry@xxxxxxx             raybry@xxxxxxxxxxxxx
The box said: "Requires Windows 98 or better",
           so I installed Linux.
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