RE: [microblaze-uclinux] thread switching problem (SCHED_RR)

[Brettschneider Falk <fbrettschneider@xxxxxxxxxxxxxxxxx>]

Hi John,
your new entry.S hasn't made problems, but hasn't helped either. :-)
But then I recompiled the whole kernel from scratch and it's much better
now.
Now I see poll() properly returns after the timeout. Sorry for maybe causing
some confusion.
Maybe my problems were reasoned in our latest switch of the CPU frequency in
a way that some time-dependent functions hadn't worked correctly anymore
until I reconfigured&recompiled the Linux kernel.

Now I just still see an almost constant delay of 9 to 15 milliseconds until
poll() reacts. Could it be the kernel reacts that slow? The microblaze is
driven with 96MHz here. From my experience, hundreds of codelines are
usually executed in 1ms.

Cheers
F@lk

> -----Original Message-----
> From: owner-microblaze-uclinux@xxxxxxxxxxxxxx
> [mailto:owner-microblaze-uclinux@xxxxxxxxxxxxxx]On Behalf Of John
> Williams
> Sent: Monday, November 14, 2005 11:24 PM
> To: microblaze-uclinux@xxxxxxxxxxxxxx
> Subject: Re: [microblaze-uclinux] thread switching problem (SCHED_RR)
> 
> 
> Hi Falk,
> 
> I haven't experimented with different scheduler strategies in uClinux
> (MicroBlaze or other), so cannot say for sure if this is a general
> uClinux thing or MicroBlaze.  Perhaps asking on uclinux-dev list might
> be helpful.
> 
> However, I can say this:
> 
> 1. The scheduler code in uClinux is the same as regular linux - so it
> should just work.
> 
> 2. I recently (last week) fixed a bug in the low level task 
> switch code
> (deep in entry.S), that may impact what you are seeing.  Can you try
> your code with a more current CVS snapshot of arch/microblaze/kernel?
> 
> Cheers,
> 
> John
> 
> 
> Brettschneider Falk wrote:
> > Hi,
> > I noticed the timeslice mechanism of SCHED_RR doesn't work correctly
> > together with poll_wait().
> > I currently use uclinux_dist&kernel CVS snapshot of October 
> 2005 but exactly
> > the same problem is with an older version of December 2004 
> that I've used
> > before.
> > 
> > situation:
> > I use the thread scheduler with SCHED_RR, 3 threads are 
> running in my app
> > started from /usr/bin.
> > Thread 1 has priority 9, thread 2 and 3 have priority 8 
> (but thread 3 is
> > inactive and sleeping on a semaphore)
> > Thread 1 sleeps on poll() with a timeout of 100ms. Function 
> poll() is a call
> > to a ucLinux driver which calls the kernel function 
> poll_wait(fd, waitqueue,
> > timeout). Thread 2 (with the lower priority) is running and 
> is heavily
> > calculating some stuff.
> > 
> > problem:
> > Linux doesn't switch to thread 1 in time after 100ms, 
> thread 2 is still
> > working even after 300ms. This shouldn't happen since 
> thread 1 has the
> > higher priority. When thread 2 finishes before 100ms are 
> over, thread 1
> > returns from poll_wait() in time.
> > It seems to me it's a bug in the ucLinux kernel that the timeout of
> > poll_wait() doesn't expire after the set 100ms. The 
> scheduler should switch
> > from thread 2 to 1 and wakes up poll_wait() in time. Am I 
> right? Has anybody
> > seen that too? Please, can anybody help? What can I do as a 
> workaround?
> > 
> > Cheers
> > F@lk
> > ___________________________
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> > Project Home Page : 
http://www.itee.uq.edu.au/~jwilliams/mblaze-uclinux
> Mailing List Archive :
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-- 

Dr John Williams, Research Fellow,
Embedded Systems Group / Reconfigurable Computing
School of ITEE, The University of Queensland, Brisbane, Australia
(p) +61 7 33652185  (f) +61 7 33654999 (m) +61 403969243
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