Messages in this thread | | | Date | Fri, 27 Aug 2010 12:09:46 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH 00/11] sched: CFS low-latency features |
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* Peter Zijlstra (peterz@infradead.org) wrote: > On Fri, 2010-08-27 at 11:21 -0400, Mathieu Desnoyers wrote: > > SIGEV_THREAD > > Upon timer expiration, invoke sigev_notify_function as if it > > were the start function of a new thread. (Among the implementa‐ > > tion possibilities here are that each timer notification could > > result in the creation of a new thread, or that a single thread > > is created to receive all notifications.) The function is > > invoked with sigev_value as its sole argument. If > > sigev_notify_attributes is not NULL, it should point to a > > pthread_attr_t structure that defines attributes for the new > > thread (see pthread_attr_init(3). > > > > So basically, it's the glibc implementation that is broken, not the standard. > > The standard is broken too, what context will the new thread inherit?
Besides pthread_attr_t, thinking of the scheduler/cgroups/etc stuff, I'd think it might be expected to inherit the state of the thread which calls timer_create(). But this is not what glibc does right now, and it is not spelled out clearly by the standard.
> The pthread_attr_t stuff tries to cover some of that, but pthread_attr_t > doesn't cover all inherited task attributes, and allows for some very > 'interesting' bugs [1].
(see below)
> > The specification also doesn't cover the case where the handler takes > more time to execute than the timer interval.
Why should it ? It seems valid for a workload to result in spawning many threads bound to more than a single core on a multi-core system. So concurrency management should be performed by the application.
> > [1] - consider the case where pthread_attr_t includes the stack and we > use a spawn thread on expire policy and then run into the situation > where the handler is delayed past the next expiration.
Setting a thread stack and generating the signal more than once is taken into account in the standard. It leads to unspecified result (IOW: don't do this):
http://www.opengroup.org/onlinepubs/009695399/functions/timer_create.html
"If evp->sigev_sigev_notify is SIGEV_THREAD and sev->sigev_notify_attributes is not NULL, if the attribute pointed to by sev->sigev_notify_attributes has a thread stack address specified by a call to pthread_attr_setstack() or pthread_attr_setstackaddr(), the results are unspecified if the signal is generated more than once."
Thanks,
Mathieu
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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