[PATCH] hrtimer: round up relative start time on low-res arches

CONFIG_TIME_LOW_RES is a temporary way for architectures to signal that
they simply return xtime in do_gettimeoffset(). In this corner-case we
want to round up by resolution when starting a relative timer, to avoid
short timeouts. This will go away with the GTOD framework.

Signed-off-by: Ingo Molnar <[e-mail]>
Cc: Roman Zippel <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/frv/Kconfig

···
 	bool
 	default n
 
+config TIME_LOW_RES
+	bool
+	default y
+
 mainmenu "Fujitsu FR-V Kernel Configuration"
 
 source "init/Kconfig"

arch/h8300/Kconfig

···
 	bool
 	default y
 
+config TIME_LOW_RES
+	bool
+	default y
+
 config ISA
 	bool
 	default y

arch/m68k/Kconfig

···
 	bool
 	default y
 
+config TIME_LOW_RES
+	bool
+	default y
+
 config ARCH_MAY_HAVE_PC_FDC
 	bool
 	depends on Q40 || (BROKEN && SUN3X)

arch/m68knommu/Kconfig

···
 	bool
 	default y
 
+config TIME_LOW_RES
+	bool
+	default y
+
 source "init/Kconfig"
 
 menu "Processor type and features"

arch/parisc/Kconfig

···
 	bool
 	default y
 
+config TIME_LOW_RES
+	bool
+	depends on SMP
+	default y
+
 config GENERIC_ISA_DMA
 	bool
 

arch/v850/Kconfig

···
 	bool
 	default y
 
+config TIME_LOW_RES
+	bool
+	default y
+
 # Turn off some random 386 crap that can affect device config
 config ISA
 	bool

kernel/hrtimer.c

···
 	/* Switch the timer base, if necessary: */
 	new_base = switch_hrtimer_base(timer, base);
 
-	if (mode == HRTIMER_REL)
+	if (mode == HRTIMER_REL) {
 		tim = ktime_add(tim, new_base->get_time());
+		/*
+		 * CONFIG_TIME_LOW_RES is a temporary way for architectures
+		 * to signal that they simply return xtime in
+		 * do_gettimeoffset(). In this case we want to round up by
+		 * resolution when starting a relative timer, to avoid short
+		 * timeouts. This will go away with the GTOD framework.
+		 */
+#ifdef CONFIG_TIME_LOW_RES
+		tim = ktime_add(tim, base->resolution);
+#endif
+	}
 	timer->expires = tim;
 
 	enqueue_hrtimer(timer, new_base);