Re: [RFC PATCH 00/11] sched: CFS low-latency features

Thomas Gleixner
2010-08-26T22:23:42Z

On Thu, 26 Aug 2010, Thomas Gleixner wrote:
> On Thu, 26 Aug 2010, Peter Zijlstra wrote:
> >
> > Fudging fork seems dubious at best, it seems generated by the use of
> > timer_create(.evp->sigev_notify = SIGEV_THREAD), which is a really
> > broken thing to do, it has very ill defined semantics and is utterly
> > unable to properly cope with error cases. Furthermore its trivial to
> > actually correctly implement the desired behaviour, so I'm really
> > skeptical on this front; friends don't let friends use SIGEV_THREAD.
>
> SIGEV_THREAD is the best proof that the whole posix timer interface
> was comitte[e]d under the influence of not to be revealed
> mind-altering substances.
>
> I completely object to add timer specific wakeup magic and support for
> braindead fork orgies to the kernel proper. All that mess can be fixed
> in user space by using sensible functionality.
>
> Providing support for misdesigned crap just for POSIX compliance
> reasons and to make some of the blind abusers of that very same crap
> happy would be a completely stupid decision.
>
> In fact that would make a brilliant precedence case for forcing the
> kernel to solve user space madness at the expense of kernel
> complexity. If we follow down that road we get requests for extra
> functionality for AIO, networking and whatever in a split second with
> no real good reason to reject them anymore.

I really risked eye cancer and digged into the glibc code.

/* There is not much we can do if the allocation fails. */
(void) pthread_create (&th, &tk->attr, timer_sigev_thread, td);

So if the helper thread which gets the signal fails to create the
thread then everything is toast.

What about fixing the f*cked up glibc implementation in the first place
instead of fiddling in the kernel to support this utter madness?

WTF can't the damned delivery thread not be created when timer_create
is called and the signal be delivered to that very thread directly via
SIGEV_THREAD_ID ?

Thanks,

tglx