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Subjectrealtime-preempt and arm
Hi all,

I'm trying the realtime-preempt patch-2.6.18-rt6 on
lh7a400 arm system with little success. In a test
program I try 5 ms timeout with select() but get 20 ms
avg or 26 ms max. When the framebuffer scrolls, the
max delay goes up to 59 ms. With a vanilla kernel I
get 10 ms (because of tick resolution?), 11 ms and 39
ms.

My question is, is the realtime-preempt patch supposed
to work on arm architecture and/or without high
resolution timer (which lh7a40x seems to lack) at all
or should I just try to be more clever.

Relevant code:

====
prio.sched_priority = 99;
if (sched_setscheduler(0, SCHED_RR, &prio) < 0) ...
if (mlockall(MCL_CURRENT | MCL_FUTURE) < 0) ...
while (1) {
t = raw_timer();
tv.tv_usec = 5000;
tv.tv_sec = 0;
select(0, 0, 0, 0, &tv);
t = raw_timer() - t;
if (max_t < t) max_t = t;
if (min_t > t) min_t = t;
avg_t += t;
++n;
if (n < 100) continue;
printf("%i revs; min: %i max: %i avg: %i\n",
n,
min_t,
max_t,
(avg_t + n / 2) / n);
====

Relevant config: PREEMPT_RT, PREEMPT_SOFTIRQS,
PREEMPT_HARDIRQS

I didnt' enable HIGH_RES_TIMERS because lh7a40x seems
not to support it.

--

tike




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