From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6941F149E0E for ; Fri, 6 Dec 2024 14:41:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733496096; cv=none; b=YyOZaIQgonnofr8/5kdck3MxXg4idj960mIxi9Yd5RYXzoedE49PGOY7usnSD7XjonfHQ4ofsG+G0LkpnuAt8O1ugf0ifn884P7SywgZWw0EN+ELZ05SKuU2jAGj4YIiFw7I4yEPH9TENc86OHeFVFulF4KD381HVMZXYUuMnsg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733496096; c=relaxed/simple; bh=7eXQpasf+bv1g4e3QuM9UngsIW4f6AEE3R15fmE36Vs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UfoskkV27R/VdHo8UVGcc/I9++euwx4/K5t4Z/nQf/egosI7gp3Nu4SJeNtvORlaTJRz1+PD6wypHwNGhg6G3JGIb80Ww/BTseD1QMtMsl4vwQ/3pH4zKza6UAWB5zXPkJPfX88jDPrYhf03tfixIdP75WyHnRCW1aAH5aAeRFk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ertCHce0; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=T5EHfQ/w; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ertCHce0"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="T5EHfQ/w" Date: Fri, 6 Dec 2024 15:41:24 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1733496085; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7eXQpasf+bv1g4e3QuM9UngsIW4f6AEE3R15fmE36Vs=; b=ertCHce0LosglRiaAjvTAyNDZlacc8uoZWeutz2Kbwdv9OEmqC+yUC2sudjOGE6/BnSKPd oSFwWuEYMkj9E94OeO88hlZxMltBhVBCsJbDz2+XQ/3A3vDo5PH5ryqAMiw7AHcjKjqWTm oujkYVbaG505p7auiYdcpfUYDYZs1tVBosqlRTQlXNYYcl9WsxISYhaM9iq0OAQ0gWFMvb AHhRVkn8EZhsaJityIdr+TrM88B8Z5R6T0KC7sXBFZ6y7bjJzjAZjpyRbULTn6WEhGGEsl Qc2p+QQ6irYA9sUdj1c7c+AygvL0uPykUDjwZWbcQYUOMk6Famd57MjYv5TL8w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1733496085; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7eXQpasf+bv1g4e3QuM9UngsIW4f6AEE3R15fmE36Vs=; b=T5EHfQ/wNeYl1rXJwUVzUPNQEBoyUKRFEvd6fyhh/6uFrSbcaqbz0aLXcCDfWWMcb0592D r5XMBO6gryd+RzAA== From: Sebastian Andrzej Siewior To: Tomas Glozar Cc: Crystal Wood , John Kacur , linux-rt-users@vger.kernel.org, williams@redhat.com Subject: Re: [PATCH v2 2/3] rt-tests: cyclictest: Support idle state disabling via libcpupower Message-ID: <20241206144124.dd-I-U47@linutronix.de> References: <20241113114509.1058593-1-tglozar@redhat.com> <20241113114509.1058593-3-tglozar@redhat.com> <0da561414289c7b929da1513962756bb8630e32f.camel@redhat.com> <20241206115201.RJsDmOXi@linutronix.de> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: On 2024-12-06 13:14:02 [+0100], Tomas Glozar wrote: > p=C3=A1 6. 12. 2024 v 12:52 odes=C3=ADlatel Sebastian Andrzej Siewior > napsal: > > What is the default behaviour and what is the intended behaviour? > > Couldn't we somehow avoid adding yet another option? >=20 > The default behavior is to hold /dev/cpu_dma_latency at zero, which > disables all idle states on all CPUs, not only those on which > cyclictest measurements are running. This has the disadvantage of a > higher power consumption than needed in most cases. With > --deepest-idle-state, idle states are limited only on CPUs cyclictest > is running on. This is a real use case? /dev/cpu_dma_latency is a big hammer to disable everything that might cause latency. So you have 4 CPUs, CPU0 is getting idle from time to time and CPU1-3 is doing RT work so it can't take sleep? > There are two reasons why we can't just use the latter and have to > have options for both. Firstly, some hardware does not support > disabling idle states on individual CPUs via the cpuidle sysfs > interface, which is used by --deepest-idle-state. Secondly, latencies > measured with --deepest-idle-state might still be higher in some cases > compared to holding /dev/cpu_dma_latency. Yes. Especially if you find power management thingy that is covered by cpu_dma_latency but not by this new switch. =20 > Tomas Sebastian