[PATCH] [2.5.35] USER_HZ & NTP problem (II)

[Rolf Fokkens]

Hi!

As said in previous postings I experimented with HZ=2048 (I actually
tried HZ=4096, don't tell anybody), and the following problem emerged:

Suppose
	HZ = 2048
and	SHIFT_SCALE = 22
and	SHIFT_UPDATE = (SHIFT_KG + MAXTC) = 12
then
	SHIFT_HZ = 11
and	(SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE) = -1

This negative number seems te be a problem for shift operations. The
following patch takes care of the problem (I hope).

Rolf

--- linux-2.5.35.orig/kernel/timer.c	Mon Sep 16 20:43:47 2002
+++ linux-2.5.35/kernel/timer.c	Mon Sep 16 21:01:41 2002
@@ -339,6 +339,11 @@
 	run_task_queue(&tq_immediate);
 }
 
+static inline long negleftshift (long val, int nshift)
+{
+    return (nshift > 0 ? val << nshift : val >> -nshift);
+}
+
 /*
  * this routine handles the overflow of the microsecond field
  *
@@ -418,7 +423,7 @@
 	if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
 	    ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
 	time_offset += ltemp;
-	time_adj = -ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
+        time_adj = negleftshift (-ltemp, SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
     } else {
 	ltemp = time_offset;
 	if (!(time_status & STA_FLL))
@@ -426,7 +431,7 @@
 	if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
 	    ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
 	time_offset -= ltemp;
-	time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
+        time_adj = negleftshift (ltemp, SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
     }
 
     /*