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 4EDEFEE49AA for ; Mon, 21 Aug 2023 15:29:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236363AbjHUP3t (ORCPT ); Mon, 21 Aug 2023 11:29:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233390AbjHUP3r (ORCPT ); Mon, 21 Aug 2023 11:29:47 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3C54FD9; Mon, 21 Aug 2023 08:29:46 -0700 (PDT) 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 D643F2F4; Mon, 21 Aug 2023 08:30:26 -0700 (PDT) Received: from [10.57.91.118] (unknown [10.57.91.118]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8253A3F740; Mon, 21 Aug 2023 08:29:43 -0700 (PDT) Message-ID: <7469ce56-b46e-54c2-faa6-5b1fddbe86ce@arm.com> Date: Mon, 21 Aug 2023 16:30:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v3 09/12] PM: EM: Add RCU mechanism which safely cleans the old data Content-Language: en-US To: Dietmar Eggemann Cc: rui.zhang@intel.com, amit.kucheria@verdurent.com, amit.kachhap@gmail.com, daniel.lezcano@linaro.org, viresh.kumar@linaro.org, len.brown@intel.com, pavel@ucw.cz, Pierre.Gondois@arm.com, ionela.voinescu@arm.com, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, rafael@kernel.org References: <20230721155022.2339982-1-lukasz.luba@arm.com> <20230721155022.2339982-10-lukasz.luba@arm.com> From: Lukasz Luba In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/16/23 14:06, Dietmar Eggemann wrote: > On 21/07/2023 17:50, Lukasz Luba wrote: >> The EM is going to support runtime modifications of the power data. >> Introduce RCU safe mechanism to clean up the old allocated EM data. >> It also adds a mutex for the EM structure to serialize the modifiers. >> >> Signed-off-by: Lukasz Luba >> --- >> kernel/power/energy_model.c | 42 +++++++++++++++++++++++++++++++++++++ >> 1 file changed, 42 insertions(+) >> >> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c >> index c2f8a0046f8a..4596bfe7398e 100644 >> --- a/kernel/power/energy_model.c >> +++ b/kernel/power/energy_model.c >> @@ -23,6 +23,9 @@ >> */ >> static DEFINE_MUTEX(em_pd_mutex); >> >> +static void em_cpufreq_update_efficiencies(struct device *dev, >> + struct em_perf_state *table); >> + >> static bool _is_cpu_device(struct device *dev) >> { >> return (dev->bus == &cpu_subsys); >> @@ -104,6 +107,45 @@ static void em_debug_create_pd(struct device *dev) {} >> static void em_debug_remove_pd(struct device *dev) {} >> #endif >> >> +static void em_destroy_rt_table_rcu(struct rcu_head *rp) >> +{ >> + struct em_perf_table *runtime_table; >> + >> + runtime_table = container_of(rp, struct em_perf_table, rcu); >> + kfree(runtime_table->state); >> + kfree(runtime_table); >> +} >> + >> +static void em_destroy_tmp_setup_rcu(struct rcu_head *rp) >> +{ >> + struct em_perf_table *runtime_table; >> + >> + runtime_table = container_of(rp, struct em_perf_table, rcu); >> + kfree(runtime_table); >> +} > > Still don't like that we have to have 2 rcu callbacks here. In case we > could assign default_table to runtime_table in em_create_pd() (and not > just default_table->state to runtime_table->state) IMHO we would only > need one rcu callback? You have convinced me. I'll change that code. > > -->8-- > > -static void em_destroy_tmp_setup_rcu(struct rcu_head *rp) > -{ > - struct em_perf_table *runtime_table; > - > - runtime_table = container_of(rp, struct em_perf_table, rcu); > - kfree(runtime_table); > -} > - > static void em_perf_runtime_table_set(struct device *dev, > struct em_perf_table *runtime_table) > { > @@ -136,13 +128,8 @@ static void em_perf_runtime_table_set(struct device *dev, > > em_cpufreq_update_efficiencies(dev, runtime_table->state); > > - /* > - * Check if the 'state' array is not actually the one from setup. > - * If it is then don't free it. > - */ > - if (tmp->state == pd->default_table->state) > - call_rcu(&tmp->rcu, em_destroy_tmp_setup_rcu); > - else > + /* Don't free default table (inital value of runtime table) */ > + if (tmp != pd->default_table) > call_rcu(&tmp->rcu, em_destroy_rt_table_rcu); > } > > @@ -349,7 +336,6 @@ static int em_create_pd(struct device *dev, int nr_states, > unsigned long flags) > { > struct em_perf_table *default_table; > - struct em_perf_table *runtime_table; > struct em_perf_domain *pd; > struct device *cpu_dev; > int cpu, ret, num_cpus; > @@ -382,24 +368,15 @@ static int em_create_pd(struct device *dev, int nr_states, > > pd->default_table = default_table; > > - runtime_table = kzalloc(sizeof(*runtime_table), GFP_KERNEL); > - if (!runtime_table) { > - kfree(default_table); > - kfree(pd); > - return -ENOMEM; > - } > - > ret = em_create_perf_table(dev, pd, nr_states, cb, flags); > if (ret) { > kfree(default_table); > - kfree(runtime_table); > kfree(pd); > return ret; > } > > - /* Re-use temporally (till 1st modification) the memory */ > - runtime_table->state = default_table->state; > - rcu_assign_pointer(pd->runtime_table, runtime_table); > + /* Initialize runtime table as default table */ > + rcu_assign_pointer(pd->runtime_table, default_table); > > if (_is_cpu_device(dev)) > for_each_cpu(cpu, cpus) { > > > I'll have to modify the unregister function to be aligned with this approach as well.