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

Peter Zijlstra
2010-08-27T15:41:39Z

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?
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].

The specification also doesn't cover the case where the handler takes
more time to execute than the timer interval.

[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.