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Message-Id: <0d92a3c45f7ffff2b0df815c4345d6e9a01cb00c.1258814214.git.wuzhangjin@gmail.com>
Date: Sat, 21 Nov 2009 22:49:12 +0800
From: Wu Zhangjin <wuzhangjin@...il.com>
To: Ralf Baechle <ralf@...ux-mips.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
Frederic Weisbecker <fweisbec@...il.com>,
Nicholas Mc Guire <der.herr@...r.at>,
David Daney <ddaney@...iumnetworks.com>,
linux-mips@...ux-mips.org, Michal Simek <monstr@...str.eu>,
Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
Wu Zhangjin <wuzhangjin@...il.com>
Subject: [PATCH v1] MIPS: Add a high precision sched_clock() via cnt32_to_63().
From: Wu Zhangjin <wuzhangjin@...il.com>
This patch adds a cnt32_to_63() and MIPS c0 count based sched_clock(),
which can provide high resolution. and also, two new kernel options are
added. the HR_SCHED_CLOCK is used to enable/disable this sched_clock(),
and the HT_SCHED_CLOCK_UPDATE is used to allow whether update the
sched_clock() automatically or not.
Without it, the Ftrace for MIPS will give useless timestamp information.
(Because cnt32_to_63() needs to be called at least once per half period
to work properly, Differ from the old version, this v1 revision set up a
kernel timer to ensure the requirement of some MIPSs which have short c0
count period.)
Signed-off-by: Wu Zhangjin <wuzhangjin@...il.com>
---
arch/mips/Kconfig | 30 ++++++++++++++++++++++
arch/mips/kernel/csrc-r4k.c | 58 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 88 insertions(+), 0 deletions(-)
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index b342197..6264f97 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1952,6 +1952,36 @@ config NR_CPUS
source "kernel/time/Kconfig"
#
+# High Resolution sched_clock() Configuration
+#
+
+config HR_SCHED_CLOCK
+ bool "High Resolution sched_clock()"
+ depends on CSRC_R4K
+ default n
+ help
+ This option enables the MIPS c0 count based high resolution
+ sched_clock().
+
+ If you need a ns precision timestamp, You are recommended to enable
+ this option. For example, If you are using the Ftrace subsystem to do
+ real time tracing, this option is needed.
+
+ If unsure, disable it.
+
+config HR_SCHED_CLOCK_UPDATE
+ bool "Update sched_clock() automatically"
+ depends on HR_SCHED_CLOCK
+ default y
+ help
+ Because Some of the MIPS c0 count period is quite short and because
+ cnt32_to_63() needs to be called at least once per half period to
+ work properly, a kernel timer is needed to set up to ensure this
+ requirement is always met.
+
+ If unusre, enable it.
+
+#
# Timer Interrupt Frequency Configuration
#
diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
index e95a3cd..5048989 100644
--- a/arch/mips/kernel/csrc-r4k.c
+++ b/arch/mips/kernel/csrc-r4k.c
@@ -6,10 +6,62 @@
* Copyright (C) 2007 by Ralf Baechle
*/
#include <linux/clocksource.h>
+#include <linux/cnt32_to_63.h>
+#include <linux/timer.h>
#include <linux/init.h>
#include <asm/time.h>
+/*
+ * MIPS' sched_clock implementation.
+ *
+ * because cnt32_to_63() needs to be called at least once per half period to
+ * work properly, and some of the MIPS' frequency is very low, perhaps a kernel
+ * timer is needed to be set up to ensure this requirement is always met.
+ * please refer to arch/arm/plat-orion/time.c and include/linux/cnt32_to_63.h
+ */
+static unsigned long __maybe_unused tclk2ns_scale;
+static unsigned long __maybe_unused tclk2ns_scale_factor;
+
+unsigned long long notrace __maybe_unused sched_clock(void)
+{
+ unsigned long long v = cnt32_to_63(read_c0_count());
+ return (v * tclk2ns_scale) >> tclk2ns_scale_factor;
+}
+
+static void __init __maybe_unused setup_sched_clock(struct clocksource *cs)
+{
+ unsigned long long v;
+
+ v = cs->mult;
+ /*
+ * We want an even value to automatically clear the top bit
+ * returned by cnt32_to_63() without an additional run time
+ * instruction. So if the LSB is 1 then round it up.
+ */
+ if (v & 1)
+ v++;
+ tclk2ns_scale = v;
+ tclk2ns_scale_factor = cs->shift;
+}
+
+static struct timer_list __maybe_unused cnt32_to_63_keepwarm_timer;
+
+static void __maybe_unused cnt32_to_63_keepwarm(unsigned long data)
+{
+ mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
+ (void) sched_clock();
+}
+
+static void __maybe_unused setup_sched_clock_update(unsigned long tclk)
+{
+ unsigned long data;
+
+ data = (0xffffffffUL / tclk / 2 - 2) * HZ;
+ setup_timer(&cnt32_to_63_keepwarm_timer, cnt32_to_63_keepwarm, data);
+ mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
+}
+
static cycle_t c0_hpt_read(struct clocksource *cs)
{
return read_c0_count();
@@ -32,7 +84,13 @@ int __init init_r4k_clocksource(void)
clocksource_set_clock(&clocksource_mips, mips_hpt_frequency);
+#ifdef CONFIG_HR_SCHED_CLOCK
+ setup_sched_clock(&clocksource_mips);
+#endif
clocksource_register(&clocksource_mips);
+#ifdef CONFIG_HR_SCHED_CLOCK_UPDATE
+ setup_sched_clock_update(mips_hpt_frequency);
+#endif
return 0;
}
--
1.6.2.1
--
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