From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD6D4EB64DD for ; Tue, 25 Jul 2023 20:46:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230423AbjGYUqw (ORCPT ); Tue, 25 Jul 2023 16:46:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230233AbjGYUqs (ORCPT ); Tue, 25 Jul 2023 16:46:48 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B5A471B0 for ; Tue, 25 Jul 2023 13:45:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690317957; 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=ePQHpPP/m2zFLGwnISEyrwq9ac4YxSfkwTurK23ce8w=; b=CFfhw5Wu8m9KOCQmYDPyCQlg7G2YlLNaF++Y66cGCywVgb3YHfcrlkg0gnT5GDig3ezJZN Wj9Z1tjKTRlFcqS2H+i+ssO4ssYbGizW9jRwsfsFpJVdQxKdukDbb8hTJTxY+ssFBfRfWK e65tl5VYkeVycEk+gEQxMBDhW/qGPSs= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-217-4NkOkLwcPZGcOnX2_xcNmQ-1; Tue, 25 Jul 2023 16:45:51 -0400 X-MC-Unique: 4NkOkLwcPZGcOnX2_xcNmQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8E3D528088A7; Tue, 25 Jul 2023 20:45:50 +0000 (UTC) Received: from [10.22.18.12] (unknown [10.22.18.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4529BF7830; Tue, 25 Jul 2023 20:45:49 +0000 (UTC) Message-ID: Date: Tue, 25 Jul 2023 16:45:49 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v5 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS Content-Language: en-US To: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , Jonathan Corbet , "Rafael J . Wysocki" Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Randy Dunlap References: <20230710194857.2898284-1-longman@redhat.com> <20230710194857.2898284-5-longman@redhat.com> From: Waiman Long In-Reply-To: <20230710194857.2898284-5-longman@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 7/10/23 15:48, Waiman Long wrote: > Commit bf5835bcdb96 ("intel_idle: Disable IBRS during long idle") > disables IBRS when the cstate is 6 or lower. However, there are > some use cases where a customer may want to use max_cstate=1 to > lower latency. Such use cases will suffer from the performance > degradation caused by the enabling of IBRS in the sibling idle thread. > Add a "ibrs_off" module parameter to force disable IBRS and the > CPUIDLE_FLAG_IRQ_ENABLE flag if set. > > In the case of a Skylake server with max_cstate=1, this new ibrs_off > option will likely increase the IRQ response latency as IRQ will now > be disabled. > > When running SPECjbb2015 with cstates set to C1 on a Skylake system. > > First test when the kernel is booted with: "intel_idle.ibrs_off" > max-jOPS = 117828, critical-jOPS = 66047 > > Then retest when the kernel is booted without the "intel_idle.ibrs_off" > added. > max-jOPS = 116408, critical-jOPS = 58958 > > That means booting with "intel_idle.ibrs_off" improves performance by: > max-jOPS: 1.2%, which could be considered noise range. > critical-jOPS: 12%, which is definitely a solid improvement. > > The admin-guide/pm/intel_idle.rst file is updated to add a description > about the new "ibrs_off" module parameter. > > Signed-off-by: Waiman Long > Acked-by: Rafael J. Wysocki > --- > Documentation/admin-guide/pm/intel_idle.rst | 17 ++++++++++++++++- > drivers/idle/intel_idle.c | 11 ++++++++++- > 2 files changed, 26 insertions(+), 2 deletions(-) Ping! Is there further suggested changes for this patch series or is it good enough to be merged? Thanks, Longman > > diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst > index b799a43da62e..39bd6ecce7de 100644 > --- a/Documentation/admin-guide/pm/intel_idle.rst > +++ b/Documentation/admin-guide/pm/intel_idle.rst > @@ -170,7 +170,7 @@ and ``idle=nomwait``. If any of them is present in the kernel command line, the > ``MWAIT`` instruction is not allowed to be used, so the initialization of > ``intel_idle`` will fail. > > -Apart from that there are four module parameters recognized by ``intel_idle`` > +Apart from that there are five module parameters recognized by ``intel_idle`` > itself that can be set via the kernel command line (they cannot be updated via > sysfs, so that is the only way to change their values). > > @@ -216,6 +216,21 @@ are ignored). > The idle states disabled this way can be enabled (on a per-CPU basis) from user > space via ``sysfs``. > > +The ``ibrs_off`` module parameter is a boolean flag (defaults to > +false). If set, it is used to control if IBRS (Indirect Branch Restricted > +Speculation) should be turned off when the CPU enters an idle state. > +This flag does not affect CPUs that use Enhanced IBRS which can remain > +on with little performance impact. > + > +For some CPUs, IBRS will be selected as mitigation for Spectre v2 and Retbleed > +security vulnerabilities by default. Leaving the IBRS mode on while idling may > +have a performance impact on its sibling CPU. The IBRS mode will be turned off > +by default when the CPU enters into a deep idle state, but not in some > +shallower ones. Setting the ``ibrs_off`` module parameter will force the IBRS > +mode to off when the CPU is in any one of the available idle states. This may > +help performance of a sibling CPU at the expense of a slightly higher wakeup > +latency for the idle CPU. > + > > .. _intel-idle-core-and-package-idle-states: > > diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c > index c9479f089037..e1b826344682 100644 > --- a/drivers/idle/intel_idle.c > +++ b/drivers/idle/intel_idle.c > @@ -69,6 +69,7 @@ static int max_cstate = CPUIDLE_STATE_MAX - 1; > static unsigned int disabled_states_mask __read_mostly; > static unsigned int preferred_states_mask __read_mostly; > static bool force_irq_on __read_mostly; > +static bool ibrs_off __read_mostly; > > static struct cpuidle_device __percpu *intel_idle_cpuidle_devices; > > @@ -1919,11 +1920,13 @@ static void state_update_enter_method(struct cpuidle_state *state, int cstate) > } > > if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) && > - state->flags & CPUIDLE_FLAG_IBRS) { > + ((state->flags & CPUIDLE_FLAG_IBRS) || ibrs_off)) { > /* > * IBRS mitigation requires that C-states are entered > * with interrupts disabled. > */ > + if (ibrs_off && (state->flags & CPUIDLE_FLAG_IRQ_ENABLE)) > + state->flags &= ~CPUIDLE_FLAG_IRQ_ENABLE; > WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); > state->enter = intel_idle_ibrs; > return; > @@ -2346,3 +2349,9 @@ MODULE_PARM_DESC(preferred_cstates, "Mask of preferred idle states"); > * 'CPUIDLE_FLAG_INIT_XSTATE' and 'CPUIDLE_FLAG_IBRS' flags. > */ > module_param(force_irq_on, bool, 0444); > +/* > + * Force the disabling of IBRS when X86_FEATURE_KERNEL_IBRS is on and > + * CPUIDLE_FLAG_IRQ_ENABLE isn't set. > + */ > +module_param(ibrs_off, bool, 0444); > +MODULE_PARM_DESC(ibrs_off, "Disable IBRS when idle");