From: Andrew Morton <akpm@linux-foundation.org>
To: Arjan van de Ven <arjan@infradead.org>
Cc: linux-kernel@vger.kernel.org, arjan@infradead.org,
lenb@kernel.org, mingo@elte.hu, yanmin_zhang@linux.intel.com,
jens.axboe@oracle.com, ink@jurassic.park.msu.ru,
Corrado Zoccolo <czoccolo@gmail.com>
Subject: Re: [PATCH v2] cpuidle: Fix the menu governor to boost IO performance
Date: Tue, 15 Sep 2009 16:23:06 -0700 [thread overview]
Message-ID: <20090915162306.66c5ce9d.akpm@linux-foundation.org> (raw)
In-Reply-To: <20090915054259.5282e5ba@infradead.org>
On Tue, 15 Sep 2009 05:42:59 +0200
Arjan van de Ven <arjan@infradead.org> wrote:
> Fix the menu idle governor which balances power savings, energy efficiency
> and performance impact.
This patch clashes a bit with
cpuidle-menu-governor-reduce-latency-on-exit.patch (which was sent to
the ACPI maintainers a month ago and ignored).
<im-fed-up-with-this-crap-ill-just-merge-it-and-if-it-breaks-dont-blame-me>
I restaged cpuidle-menu-governor-reduce-latency-on-exit.patch so it
goes after cpuidle-fix-the-menu-governor-to-boost-io-performance.patch.
perhaps you could take a look at Corrado's change?
From: Corrado Zoccolo <czoccolo@gmail.com>
Move the state residency accounting and statistics computation off the hot
exit path.
On exit, the need to recompute statistics is recorded, and new statistics
will be computed when menu_select is called again.
The expected effect is to reduce processor wakeup latency from sleep
(C-states). We are speaking of few hundreds of cycles reduction out of a
several microseconds latency (determined by the hardware transition), so
it is difficult to measure.
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Adam Belay <abelay@novell.com
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
drivers/cpuidle/governors/menu.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff -puN drivers/cpuidle/governors/menu.c~cpuidle-menu-governor-reduce-latency-on-exit drivers/cpuidle/governors/menu.c
--- a/drivers/cpuidle/governors/menu.c~cpuidle-menu-governor-reduce-latency-on-exit
+++ a/drivers/cpuidle/governors/menu.c
@@ -96,6 +96,7 @@
struct menu_device {
int last_state_idx;
+ int needs_update;
unsigned int expected_us;
u64 predicted_us;
@@ -166,6 +167,8 @@ static inline int performance_multiplier
static DEFINE_PER_CPU(struct menu_device, menu_devices);
+static void menu_update(struct cpuidle_device *dev);
+
/**
* menu_select - selects the next idle state to enter
* @dev: the CPU
@@ -180,6 +183,11 @@ static int menu_select(struct cpuidle_de
data->last_state_idx = 0;
data->exit_us = 0;
+ if (data->needs_update) {
+ menu_update(dev);
+ data->needs_update = 0;
+ }
+
/* Special case when user has set very strict latency requirement */
if (unlikely(latency_req == 0))
return 0;
@@ -231,7 +239,7 @@ static int menu_select(struct cpuidle_de
}
/**
- * menu_reflect - attempts to guess what happened after entry
+ * menu_reflect - records that data structures need update
* @dev: the CPU
*
* NOTE: it's important to be fast here because this operation will add to
@@ -240,6 +248,16 @@ static int menu_select(struct cpuidle_de
static void menu_reflect(struct cpuidle_device *dev)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
+ data->needs_update = 1;
+}
+
+/**
+ * menu_update - attempts to guess what happened after entry
+ * @dev: the CPU
+ */
+static void menu_update(struct cpuidle_device *dev)
+{
+ struct menu_device *data = &__get_cpu_var(menu_devices);
int last_idx = data->last_state_idx;
unsigned int last_idle_us = cpuidle_get_last_residency(dev);
struct cpuidle_state *target = &dev->states[last_idx];
_
next prev parent reply other threads:[~2009-09-15 23:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-15 3:42 [PATCH v2] cpuidle: Fix the menu governor to boost IO performance Arjan van de Ven
2009-09-15 3:54 ` Andrew Morton
2009-09-15 4:15 ` Arjan van de Ven
2009-09-15 4:18 ` Arjan van de Ven
2009-09-15 5:03 ` Rik van Riel
2009-09-15 23:23 ` Andrew Morton [this message]
2009-09-16 4:35 ` Arjan van de Ven
2009-09-17 13:39 ` Arjan van de Ven
2009-11-04 9:39 ` Corrado Zoccolo
2009-11-08 20:40 ` Arjan van de Ven
2009-11-08 21:59 ` Corrado Zoccolo
2009-11-08 22:30 ` Arjan van de Ven
2009-11-09 13:29 ` Corrado Zoccolo
2009-11-08 22:39 ` Arjan van de Ven
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