[RFC patch 05/15] get_cycles() : MIPS HAVE_GET_CYCLES_32

Mathieu Desnoyers
2008-10-17T00:07:12Z

[-- Attachment #1: get-cycles-mips-have-get-cycles.patch --]
[-- Type: text/plain, Size: 2827 bytes --]

partly reverts commit efb9ca08b5a2374b29938cdcab417ce4feb14b54. Selects
HAVE_GET_CYCLES_32 only on CPUs where it is safe to use it.

Currently consider the "_WORKAROUND" cases for 4000 and 4400 to be unsafe, but
should probably add other sub-architecture to the blacklist.

Do not define HAVE_GET_CYCLES because MIPS does not provide 64-bit tsc (only
32-bits).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Ralf Baechle <ralf@linux-mips.org>
CC: David Miller <davem@davemloft.net>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: linux-arch@vger.kernel.org
---
arch/mips/Kconfig | 4 ++++
include/asm-mips/timex.h | 25 +++++++++++++++++++++++++
2 files changed, 29 insertions(+)

Index: linux-2.6-lttng/include/asm-mips/timex.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-mips/timex.h 2008-10-16 12:25:47.000000000 -0400
+++ linux-2.6-lttng/include/asm-mips/timex.h 2008-10-16 12:34:18.000000000 -0400
@@ -29,14 +29,39 @@
* which isn't an evil thing.
*
* We know that all SMP capable CPUs have cycle counters.
+ *
+ * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * HAVE_GET_CYCLES makes sure that this case is handled properly :
+ *
+ * Ralf Baechle <ralf@linux-mips.org> :
+ * This avoids us executing an mfc0 c0_count instruction on processors which
+ * don't have but also on certain R4000 and R4400 versions where reading from
+ * the count register just in the very moment when its value equals c0_compare
+ * will result in the timer interrupt getting lost.
*/

typedef unsigned int cycles_t;

+#ifdef HAVE_GET_CYCLES_32
+static inline cycles_t get_cycles(void)
+{
+ return read_c0_count();
+}
+
+static inline void get_cycles_barrier(void)
+{
+}
+
+static inline cycles_t get_cycles_rate(void)
+{
+ return CLOCK_TICK_RATE;
+}
+#else
static inline cycles_t get_cycles(void)
{
return 0;
}
+#endif

#endif /* __KERNEL__ */

Index: linux-2.6-lttng/arch/mips/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/mips/Kconfig 2008-10-16 12:25:47.000000000 -0400
+++ linux-2.6-lttng/arch/mips/Kconfig 2008-10-16 12:34:01.000000000 -0400
@@ -1581,6 +1581,10 @@ config CPU_R4000_WORKAROUNDS
config CPU_R4400_WORKAROUNDS
bool

+config HAVE_GET_CYCLES_32
+ def_bool y
+ depends on !CPU_R4400_WORKAROUNDS
+
#
# Use the generic interrupt handling code in kernel/irq/:
#

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal