From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id BD947364A0; Fri, 16 Aug 2024 16:31:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723825899; cv=none; b=IfP3cIJqT80Ws+c1nrivq1/oG+imwKyy6Y04oyKKWY9W0a84ssYJGlKfgQAUMqJQ2n5rJVA6ex/yuRE0e60bngtl3LFo1bP1mnLWYABaF/6HmR8e2AIQvGYrngPgXFCEEdRbwiM4uLAwfyGYuruE93mwsejSGJ39y9/ehIIX/Lo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723825899; c=relaxed/simple; bh=9PT3gNpyR9fSzfxTZR3Nyw668zUlJjUTQe2irAaX7G0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pLUG5MMIb8BiJS9+otPuZwhYB2oYHwTmshdUnVi0U61Z2P1uCq/U/Q9oTLu5/LiA6aKFE13YVOcK51vn2oE+CtqO4xzdV1oRHGhitV5+FVCOEfgnaHhKSNPr5jJBz+dMwjDP5o2ZInrHSXKSMpRoS7aqxKiYqv5p8UxYeSlC0KM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5D4BB152B; Fri, 16 Aug 2024 09:32:03 -0700 (PDT) Received: from [10.1.196.28] (eglon.cambridge.arm.com [10.1.196.28]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5A0563F58B; Fri, 16 Aug 2024 09:31:33 -0700 (PDT) Message-ID: <983fded5-48f8-439d-8afe-45b60841985a@arm.com> Date: Fri, 16 Aug 2024 17:31:33 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 19/22] x86/resctrl: Introduce the interface to switch between monitor modes Content-Language: en-GB To: Babu Moger Cc: x86@kernel.org, hpa@zytor.com, paulmck@kernel.org, rdunlap@infradead.org, tj@kernel.org, peterz@infradead.org, yanjiewtw@gmail.com, kim.phillips@amd.com, lukas.bulwahn@gmail.com, seanjc@google.com, jmattson@google.com, leitao@debian.org, jpoimboe@kernel.org, rick.p.edgecombe@intel.com, kirill.shutemov@linux.intel.com, jithu.joseph@intel.com, kai.huang@intel.com, kan.liang@linux.intel.com, daniel.sneddon@linux.intel.com, pbonzini@redhat.com, sandipan.das@amd.com, ilpo.jarvinen@linux.intel.com, peternewman@google.com, maciej.wieczor-retman@intel.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, eranian@google.com, mingo@redhat.com, bp@alien8.de, corbet@lwn.net, dave.hansen@linux.intel.com, fenghua.yu@intel.com, reinette.chatre@intel.com, tglx@linutronix.de References: <784eaa900b9e0778ddc534c04c7ded9466bfd19b.1722981659.git.babu.moger@amd.com> From: James Morse In-Reply-To: <784eaa900b9e0778ddc534c04c7ded9466bfd19b.1722981659.git.babu.moger@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Babu, On 06/08/2024 23:00, Babu Moger wrote: > Introduce interface to switch between ABMC and legacy modes. > > By default ABMC is enabled on boot if the feature is available. > Provide the interface to go back to legacy mode if required. I may have missed it on an earlier version ... why would anyone want the non-ABMC behaviour on hardware that requires it: counters randomly reset and randomly return 'Unavailable'... is that actually useful? You default this to on, so there isn't a backward compatibility argument here. It seems like being able to disable this is a source of complexity - is it needed? For MPAM I'm looking at enabling this on any platform that is short of monitors. If user-space disables it I don't have a "at random" hardware behaviour to fall back on - its extra work to invent a behaviour I'm not sure is useful... > $ cat /sys/fs/resctrl/info/L3_MON/mbm_mode > [mbm_cntr_assign] > legacy > > To enable the "mbm_cntr_assign" mode: > $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_mode > > To enable the legacy monitoring feature: > $ echo "legacy" > /sys/fs/resctrl/info/L3_MON/mbm_mode > > MBM event counters will reset when mbm_mode is changed. Thanks, James