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From: Pierre Ossman <drzeus-list@drzeus.cx>
To: "LKML" <linux-kernel@vger.kernel.org>,
	linux-pm@lists.linux-foundation.org, "Pallipadi,
	Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: "Dave Jones" <davej@codemonkey.org.uk>,
	"Andi Kleen" <andi@firstfloor.org>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	"Adam Belay" <abelay@novell.com>,
	"Lee Revell" <rlrevell@joe-job.com>,
	"Pavel Machek" <pavel@ucw.cz>
Subject: Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
Date: Tue, 11 Mar 2008 08:51:45 +0100	[thread overview]
Message-ID: <20080311085145.5fcf3186@mjolnir.drzeus.cx> (raw)
In-Reply-To: <20080309151659.63d54f38@mjolnir.drzeus.cx>

I had a sudden surge of inspiration and decided to follow up on this
one a bit: 

> 
> 5. Second core
> 
> Disabling the second core makes the noise go away. This might be a subset of 1., as I've been told that a stopped core enters C1.
> 

I have now found a very hacky workaround that is slightly better than
disabling C3 altogether; making C3 exclusive to one core at a time. It
seems to kill the noise and the system now spends 50% in C3, instead of
0%.

I read somewhere that the Intel Duo:s have an extra low power mode that
is entered if both cores are suspended at the same time (disabling the
shared cache or something like that I guess). So perhaps that mode is
the culprit. I'm hoping there's a way to disable just that feature. Do
any of you know a way? Venkatesh perhaps?

Here's the patch I'm currently running at least:

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 78d77c5..9a859fb 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -16,6 +16,8 @@
 
 #define BREAK_FUZZ     4       /* 4 us */
 
+static atomic_t cur_deep_cpu = ATOMIC_INIT(-1);
+
 struct menu_device {
        int             last_state_idx;
 
@@ -50,6 +52,13 @@ static int menu_select(struct cpuidle_device *dev)
                        break;
                if (s->exit_latency > pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY))
                        break;
+
+               if (s->flags & CPUIDLE_FLAG_DEEP) {
+                       rmb();
+                       if (atomic_cmpxchg(&cur_deep_cpu, -1, dev->cpu) != -1)
+                               break;
+                       wmb();
+               }
        }
 
        data->last_state_idx = i - 1;
@@ -80,6 +89,11 @@ static void menu_reflect(struct cpuidle_device *dev)
        if (!(target->flags & CPUIDLE_FLAG_TIME_VALID))
                measured_us = USEC_PER_SEC / HZ;
 
+       if (atomic_read(&cur_deep_cpu) == dev->cpu) {
+               atomic_set(&cur_deep_cpu, -1);
+               wmb();
+       }
+
        /* Predict time remaining until next break event */
        if (measured_us + BREAK_FUZZ < data->expected_us - target->exit_latency) {
                data->predicted_us = max(measured_us, data->last_measured_us);


-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org

  parent reply	other threads:[~2008-03-11  7:52 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-29 18:38 [RFC][PATCH] " Pierre Ossman
2008-02-29 21:44 ` Lennart Sorensen
2008-03-01 12:31   ` Pierre Ossman
2008-03-01 13:40 ` Pierre Ossman
2008-03-02  2:27 ` Lee Revell
2008-03-02 14:17   ` Pierre Ossman
2008-03-03 12:36 ` Andi Kleen
2008-03-03 20:18 ` [PATCH] " Pierre Ossman
2008-03-03 20:46   ` Pavel Machek
2008-03-03 21:03     ` Pierre Ossman
2008-03-03 21:08       ` Pavel Machek
2008-03-03 21:14         ` Pallipadi, Venkatesh
2008-03-03 21:17           ` Pierre Ossman
2008-03-03 22:04             ` Pallipadi, Venkatesh
2008-03-03 23:05               ` [linux-pm] " Alan Stern
2008-03-03 23:10                 ` Andi Kleen
2008-03-04  4:00                   ` Dave Jones
2008-03-04  6:14                     ` Pierre Ossman
2008-03-04 17:19                       ` Pierre Ossman
2008-03-04 17:29                         ` Andi Kleen
2008-03-04 17:30                           ` Pierre Ossman
2008-03-04 17:43                             ` Andi Kleen
2008-03-04 18:04                               ` Pierre Ossman
2008-03-04 18:34                                 ` Andi Kleen
2008-03-05  6:04                                   ` Pierre Ossman
2008-03-05 15:48                                     ` Andi Kleen
2008-03-05 16:53                                       ` Pierre Ossman
2008-03-05 17:32                                         ` Andi Kleen
2008-03-04 19:01                         ` Pallipadi, Venkatesh
2008-03-05  6:02                           ` Pierre Ossman
2008-03-05  8:40                             ` Pierre Ossman
2008-03-05  9:03                               ` Pavel Machek
2008-03-05 13:42                                 ` Pierre Ossman
2008-03-05 13:47                                   ` Pavel Machek
2008-03-05 13:52                                     ` Pierre Ossman
2008-03-06  8:27                               ` Pierre Ossman
2008-03-09 14:16                                 ` Pierre Ossman
2008-03-09 18:19                                   ` Rafael J. Wysocki
2008-03-09 18:50                                   ` Alan Stern
2008-03-09 19:30                                   ` Henrique de Moraes Holschuh
2008-03-09 20:14                                     ` Pierre Ossman
2008-03-09 20:41                                       ` Henrique de Moraes Holschuh
2008-03-09 20:54                                         ` Henrique de Moraes Holschuh
2008-03-10 10:00                                   ` Pavel Machek
2008-03-10 12:49                                     ` Pierre Ossman
2008-03-10 13:04                                       ` Andi Kleen
2008-03-10 13:29                                         ` Pierre Ossman
2008-03-12 19:11                                       ` Len Brown
2008-03-13  8:10                                         ` Pavel Machek
2008-03-13 10:42                                           ` Andi Kleen
2008-03-14  4:13                                             ` Len Brown
2008-03-13 16:34                                         ` Pierre Ossman
2008-03-13 16:47                                           ` Pallipadi, Venkatesh
2008-03-13 17:44                                             ` Pierre Ossman
2008-03-13 17:49                                           ` Pierre Ossman
2008-03-14 19:40                                           ` Pierre Ossman
2008-03-14 21:15                                             ` Pallipadi, Venkatesh
2008-03-15  0:41                                               ` Pierre Ossman
2008-03-11  7:51                                   ` Pierre Ossman [this message]
2008-03-11 10:48                                     ` Andi Kleen
2008-03-11 15:20                                       ` Pierre Ossman
2008-03-11 17:31                                         ` Pierre Ossman
2008-03-12 19:17                                       ` Len Brown
2008-03-12 20:31                               ` Len Brown
2008-03-04  9:40                     ` Andi Kleen
2008-03-03 23:09               ` Andi Kleen

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