Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758961AbYCCUUi (ORCPT ); Mon, 3 Mar 2008 15:20:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751897AbYCCUUK (ORCPT ); Mon, 3 Mar 2008 15:20:10 -0500 Received: from gateway.drzeus.cx ([85.8.24.16]:52093 "EHLO smtp.drzeus.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751008AbYCCUUI (ORCPT ); Mon, 3 Mar 2008 15:20:08 -0500 Date: Mon, 3 Mar 2008 21:18:42 +0100 From: Pierre Ossman To: Venkatesh Pallipadi , Adam Belay Cc: linux-pm@lists.linux-foundation.org, LKML , Andi Kleen , "Lee Revell" Subject: [PATCH] cpuidle: avoid singing capacitors Message-ID: <20080303211842.6f492782@mjolnir.drzeus.cx> In-Reply-To: <20080229193812.31f45b0c@mjolnir.drzeus.cx> References: <20080229193812.31f45b0c@mjolnir.drzeus.cx> X-Mailer: Claws Mail 3.3.1 (GTK+ 2.12.8; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3164 Lines: 84 Many devices today are of a less than stellar quality, and singing capacitors are a common problem. A high-pitch noise is created, caused by power fluctuations as the processor enters and leaves deep sleep at a high frequency. Instead of just disabling the deep sleep (which wastes power). This patch merely reduces the number of times it is entered so that the frequency doesn't exceed 500 Hz. That should make sure the problem is inaudible. Signed-off-by: Pierre Ossman -- I've been playing around with this for a bit, and the jiffies approach just had too many gotchas. So I tried using the information that was already present in the menu governor. This is what I came up with. It solves the primary problem of getting rid of the noise. I've also tried some crude power measurements and I couldn't get any difference with and without the patch. Powertop also nicely shows that the CPU is still spending almost all of its time in C3. Therefore, I'm letting the effects of it be enabled by default. So I'm taking the [RFC] off it. Please still test and see that it solves the issue on other machines, and the it does not cause any big power surges. diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index 78d77c5..d9c43e3 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -16,6 +16,8 @@ #define BREAK_FUZZ 4 /* 4 us */ +static unsigned int min_deep_sleep = 2000; + struct menu_device { int last_state_idx; @@ -50,6 +52,19 @@ static int menu_select(struct cpuidle_device *dev) break; if (s->exit_latency > pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY)) break; + + /* + * In order to avoid the problem of "singing capacitors", + * don't enter a deep sleep for short durations (by + * default, nothing shorter than 2 ms). This will, + * hopefully, keep the problem inaudible. + */ + if (s->flags & CPUIDLE_FLAG_DEEP) { + if (min_deep_sleep > data->expected_us) + break; + if (min_deep_sleep > data->predicted_us) + break; + } } data->last_state_idx = i - 1; @@ -132,6 +147,9 @@ static void __exit exit_menu(void) cpuidle_unregister_governor(&menu_governor); } +module_param(min_deep_sleep, uint, 0644) +MODULE_PARM_DESC(min_deep_sleep, "min time (us) to spend in deep sleep to avoid noise") + MODULE_LICENSE("GPL"); module_init(init_menu); module_exit(exit_menu); -- -- Pierre Ossman Linux kernel, MMC maintainer http://www.kernel.org PulseAudio, core developer http://pulseaudio.org rdesktop, core developer http://www.rdesktop.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/