From: Steven Rostedt <rostedt@goodmis.org>
To: Simon White <s_a_white@email.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Best Kernel Timers?
Date: Wed, 28 Sep 2005 05:53:33 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.58.0509280547540.5529@localhost.localdomain> (raw)
In-Reply-To: <20050928093602.DFA0B8401C@ws1-5.us4.outblaze.com>
On Wed, 28 Sep 2005, Simon White wrote:
> Hi,
>
> Wondered if anyone could provide information about where to look for
> suitable kernel timers?
Have you taken a look at what is being done by Thomas Gleixner?
http://lwn.net/Articles/152363/
Also you may be interested in Ingo Molnar's RT kernel.
http://people.redhat.com/mingo/realtime-preempt/
As well as the work being done by the HRT folks.
http://sourceforge.net/projects/high-res-timers
-- Steve
>
> For a while I have been working on supporting the hardsid/catweasel
> cards on Linux (and Windows). Although undesirable the original
> implementations required real usec delays in the OS
> (this requirement being fixed in the very latest hardware). I know
> Linux is not realtime so the original drivers were designed to
> queue hardware writes to a realtime thread that busy waited and
> recovered as best it could from errors (on the whole this worked
> pretty well). Also another version of the code was written to use
> rtlinux/rtai that was capable of non busy waiting.
>
> More recently with the release of the new buffering hardware the
> driver was redesigned from the realtime posix code. Due to these
> changes the busy waiting (for the old cards) can nolonger occur
> and the delays have to happen asynchronusly notifing the realtime
> thread when the delay has expired. The code uses the posix
> timer_set, etc calls with realtime clock with absolute delays and
> flags a semaphore when the signal occurs (works great under
> realtime systems).
>
> Now as an alternative it is again desired that a version (although
> wont perfectly work) be available to a vanilla 2.6 kernel (possibly
> 2.4) with similiar limitations as before. Its a shame the posix
> calls appear to not be supported in kernel for drivers so I have
> wrapped the calls for semaphores/mutexs/threads to kernel
> equivalents.
>
> However I have no idea what to do for the timers. Is there
> something suitable inkernel that would provide an async callback
> to pre-empt a realtime thread and provide better resolution than
> HZ a far amount of the time? Or do I have to run a seperate lower
> priority busy waiting thread to wakeup the realtime one?
>
> Advice appreciated.
> Simon
>
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next prev parent reply other threads:[~2005-09-28 9:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-28 9:36 Best Kernel Timers? Simon White
2005-09-28 9:53 ` Steven Rostedt [this message]
2005-09-28 17:33 ` Christoph Lameter
2005-09-28 10:08 Simon White
2005-09-28 11:17 ` Steven Rostedt
2005-09-28 17:34 ` Christoph Lameter
2005-09-28 11:55 Simon White
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