Some problems with the libbsd update

[Joel Sherrill]

On Wed, Aug 22, 2018, 4:51 AM Sebastian Huber <
sebastian.huber at embedded-brains.de> wrote:

> On 22/08/18 09:50, Sebastian Huber wrote:
> > To support everything in RTEMS is a lot of work, so I have to make
> > some trade-offs. The implementation of this API must be as efficient
> > as possible since it is used in the critical paths of the network
> > stack. I will try to use a single global epoch and thread-specific
> > records as suggested by Matthew Macy to avoid the need for
> > per-processor data structures and the thread pinning. One key issue is
> > that epoch records must not be destroyed:
> >
> > https://www.mankier.com/3/ck_epoch_register
> >
> > The consequence of this is that unlimited thread objects may lead to
> > undefined behaviour with this implementation approach. Also
> > thread-local storage cannot be used since it is reinitialized once a
> > thread restarted or reused. The epoch record must be included in the
> > Thread_Control and must not be touched by _Thread_Initialize(). This
> > means I have to move the API and its implementation along with the
> > Concurrency Kit to RTEMS.
>
> Ok, there is also an
>
> http://www.concurrencykit.org/doc/ck_epoch_unregister.html
>
> and
>
> http://www.concurrencykit.org/doc/ck_epoch_recycle.html
>
> This allows a localized implementation in libbsd.
>
> Due to performance reasons this requires the use of thread-local
> storage. Any objections to make thread-local storage a hard requirement
> for libbsd support?
>

Not particularly but there should be an effort to identify which targets do
not have TLS support yet. Other than sparc, arm, powerpc and i386, I don't
know the status. Sounds like a series of tickets.

Certainly seems like the mist straightforward approach to solving the
problem. But it requires some work on TLS which was needed anyway.

>
> --
> Sebastian Huber, embedded brains GmbH
>
> Address : Dornierstr. 4, D-82178 Puchheim, Germany
> Phone   : +49 89 189 47 41-16
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> E-Mail  : sebastian.huber at embedded-brains.de
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>
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>
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