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Date: Sat, 25 Sep 2010 17:30:49 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: [Xenomai-core] RFC: /proc/xenomai/latency change
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Hi,

I have been working on omap3 performances, and during this, I noticed 
one flaw in /proc/xenomai/latency: it displays the whole timer subsystem
anticipation whereas it should probably only allow setting the scheduler
latency. The reason is that when issuing the customary:
echo 0 > /proc/xenomai/latency

we were in fact also disabling any account of the timer programming 
latency. This is probably almoste invisible on systems with low timer 
programming latencies, but this turned out to account for around 5us 
error on timer programming on omap. Now, the timer programming latency 
is back to a more reasonable 1us on omap, but I still think we should 
change this.

However, since it may break some users settings, I wonder if we should 
apply it now or only in the 2.6 branch.

Here is the patch I am talking about:
diff --git a/ksrc/nucleus/pod.c b/ksrc/nucleus/pod.c
index 7db0ccf..485dbef 100644
--- a/ksrc/nucleus/pod.c
+++ b/ksrc/nucleus/pod.c
@@ -3164,7 +3164,7 @@ static int latency_read_proc(char *page,
 {
        int len;

-       len = sprintf(page, "%Lu\n", xnarch_tsc_to_ns(nklatency));
+       len = sprintf(page, "%Lu\n", xnarch_tsc_to_ns(nklatency) - nktimerlat);
        len -= off;
        if (len <= off + count)
                *eof = 1;
@@ -3196,7 +3196,7 @@ static int latency_write_proc(struct file *file,
        if ((*end != '\0' && !isspace(*end)) || ns < 0)
                return -EINVAL;

-       nklatency = xnarch_ns_to_tsc(ns);
+       nklatency = xnarch_ns_to_tsc(ns + nktimerlat);

        return count;
 }


-- 
                                                                Gilles.