From patchwork Thu Jan 21 00:35:50 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Giovanni Gherdovich X-Patchwork-Id: 368356 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 508CAC4321A for ; Thu, 21 Jan 2021 02:09:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 350D82388E for ; Thu, 21 Jan 2021 02:09:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728574AbhAUAwX (ORCPT ); Wed, 20 Jan 2021 19:52:23 -0500 Received: from mx2.suse.de ([195.135.220.15]:56374 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726671AbhAUAgl (ORCPT ); Wed, 20 Jan 2021 19:36:41 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 5E99DAC9B; Thu, 21 Jan 2021 00:35:59 +0000 (UTC) From: Giovanni Gherdovich To: Borislav Petkov , Ingo Molnar , Peter Zijlstra , "Rafael J . Wysocki" , Viresh Kumar Cc: Jon Grimm , Nathan Fontenot , Yazen Ghannam , Thomas Lendacky , Suthikulpanit Suravee , Mel Gorman , Pu Wen , Juri Lelli , Vincent Guittot , Dietmar Eggemann , x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, Giovanni Gherdovich Subject: [PATCH] x86, sched: On AMD EPYC set freq_max = max_boost in schedutil invariant formula Date: Thu, 21 Jan 2021 01:35:50 +0100 Message-Id: <20210121003550.20415-1-ggherdovich@suse.cz> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Phoronix.com discovered a severe performance regression on AMD APYC introduced on schedutil [see link 1] by the following commits from v5.11-rc1 commit 41ea667227ba ("x86, sched: Calculate frequency invariance for AMD systems") commit 976df7e5730e ("x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC") Furthermore commit db865272d9c4 ("cpufreq: Avoid configuring old governors as default with intel_pstate") from v5.10 made it extremely easy to default to schedutil even if the preferred driver is acpi_cpufreq. Distros are likely to build both intel_pstate and acpi_cpufreq on x86, and the presence of the former removes ondemand from the defaults. This situation amplifies the visibility of the bug we're addressing. [link 1] https://www.phoronix.com/scan.php?page=article&item=linux511-amd-schedutil&num=1 1. PROBLEM DESCRIPTION : over-utilization and schedutil 2. PROPOSED SOLUTION : raise freq_max in schedutil formula 3. DATA TABLE : image processing benchmark 4. ANALYSIS AND COMMENTS : with over-utilization, freq-invariance is lost 1. PROBLEM DESCRIPTION (over-utilization and schedutil) The problem happens on CPU-bound workloads spanning a large number of cores. In this case schedutil won't select the maximum P-State. Actually, it's likely that it will select the minimum one. A CPU-bound workload puts the machine in a state generally called "over-utilization": an increase in CPU speed doesn't result in an increase of capacity. The fraction of time tasks spend on CPU becomes constant regardless of clock frequency (the tasks eat whatever we throw at them), and the PELT invariant util goes up and down with the frequency (i.e. it's not invariant anymore). 2. PROPOSED SOLUTION (raise freq_max in schedutil formula) The solution we implement here is a stop-gap one: when the driver is acpi_cpufreq and the machine an AMD EPYC, schedutil will use max_boost instead of max_P as the value for freq_max in its formula freq_next = 1.25 * freq_max * util essentially giving freq_next some more headroom to grow in the over-utilized case. This is the approach also followed by intel_pstate in passive mode. The correct way to attack this problem would be to have schedutil detect over-utilization and select freq_max irrespective of the util value, which has no meaning at that point. This approach is too risky for an -rc5 submission so we defer it to the next cycle. 3. DATA TABLE (image processing benchmark) What follow is a more detailed account of the effects on a specific test. TEST : Intel Open Image Denoise, www.openimagedenoise.org INVOCATION : ./denoise -hdr memorial.pfm -out out.pfm -bench 200 -threads $NTHREADS CPU : MODEL : 2x AMD EPYC 7742 FREQUENCY TABLE : P2: 1.50 GHz P1: 2.00 GHz P0: 2.25 GHz MAX BOOST : 3.40 GHz Results: threads, msecs (ratio). Lower is better. v5.10 v5.11-rc4 v5.11-rc4-patch ------------------------------------------------------- 1 1069.85 (1.00) 1071.84 (1.00) 1070.42 (1.00) 2 542.24 (1.00) 544.40 (1.00) 544.48 (1.00) 4 278.00 (1.00) 278.44 (1.00) 277.72 (1.00) 8 149.81 (1.00) 149.61 (1.00) 149.87 (1.00) 16 79.01 (1.00) 79.31 (1.00) 78.94 (1.00) 24 58.01 (1.00) 58.51 (1.01) 58.15 (1.00) 32 46.58 (1.00) 48.30 (1.04) 46.66 (1.00) 48 37.29 (1.00) 51.29 (1.38) 37.27 (1.00) 64 34.01 (1.00) 49.59 (1.46) 33.71 (0.99) 80 31.09 (1.00) 44.27 (1.42) 31.33 (1.01) 96 28.56 (1.00) 40.82 (1.43) 28.47 (1.00) 112 28.09 (1.00) 40.06 (1.43) 28.63 (1.02) 120 28.73 (1.00) 39.78 (1.38) 28.14 (0.98) 128 28.93 (1.00) 39.60 (1.37) 29.38 (1.02) See how the 128 threads case is almost 40% worse than baseline in v5.11-rc4. 4. ANALYSIS AND COMMENTS (with over-utilization freq-invariance is lost) Statistics for NTHREADS=128 (number of physical cores of the machine) v5.10 v5.11-rc4 ------------------------ CPU activity (mpstat) 80-90% 80-90% schedutil requests (tracepoint) always P0 mostly P2 CPU frequency (HW feedback) ~2.2 GHz ~1.5 GHz PELT root rq util (tracepoint) ~825 ~450 mpstat shows that the workload is CPU-bound and usage doesn't change with clock speed. What is striking is that the PELT util of any root runqueue in v5.11-rc4 is half of what used to be before the frequency invariant support (v5.10), leading to wrong frequency choices. How did we get there? This workload is constant in time, so instead of using the PELT sum we can pretend that scale invariance is obtained with util_inv = util_raw * freq_curr / freq_max1 [formula-1] where util_raw is the PELT util from v5.10 (which is to say, not invariant), and util_inv is the PELT util from v5.11-rc4. freq_max1 comes from commit 976df7e5730e ("x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC") and is (P0+max_boost)/2 = (2.25+3.4)/2 = 2.825 GHz. Then we have the schedutil formula freq_next = 1.25 * freq_max2 * util_inv [formula-2] Here v5.11-rc4 uses freq_max2 = P0 = 2.25 GHz (and this patch changes it to 3.4 GHz). Since all cores are busy, there is no boost available. Let's be generous and say the tasks initially get P0, i.e. freq_curr = 2.25 GHz. Combining the formulas above and taking util_raw = 825/1024 = 0.8, freq_next is: freq_next = 1.25 * 2.25 * 0.8 * 2.25 / 2.825 = 1.79 GHz After quantization (pick the next frequency up in the table), freq_next is P1 = 2.0 GHz. See how we lost 250 MHz in the process. Iterate once more, freq_next become 1.59 GHz. Since it's > P2, it's saved by quantization and P1 is selected, but if util_raw fluctuates a little and goes below 0.75, P0 is selected and that kills util_inv by formula-1, which gives util_inv = 0.4. The culprit of the problem is that with over-utilization, util_raw and freq_curr in formula-1 are independent. In the nominal case, if freq_curr goes up then util_raw goes down and viceversa. Here util_raw doesn't care and stays constant. If freq_curr descrease, util_inv decreases too and so forth (it's a feedback loop). Fixes: 41ea667227ba ("x86, sched: Calculate frequency invariance for AMD systems") Fixes: 976df7e5730e ("x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC") Signed-off-by: Giovanni Gherdovich --- drivers/cpufreq/freq_table.c | 51 ++++++++++++++++++++++++++++++++ include/linux/cpufreq.h | 5 ++++ kernel/sched/cpufreq_schedutil.c | 8 +++-- 3 files changed, 62 insertions(+), 2 deletions(-) diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c index f839dc9852c0..f143c7db9d85 100644 --- a/drivers/cpufreq/freq_table.c +++ b/drivers/cpufreq/freq_table.c @@ -10,6 +10,10 @@ #include #include +#ifdef CONFIG_ACPI_CPPC_LIB +#include +#endif + /********************************************************************* * FREQUENCY TABLE HELPERS * *********************************************************************/ @@ -29,12 +33,53 @@ bool policy_has_boost_freq(struct cpufreq_policy *policy) } EXPORT_SYMBOL_GPL(policy_has_boost_freq); +#ifdef CONFIG_ACPI_CPPC_LIB +static bool amd_max_boost(unsigned int max_freq, unsigned int *max_boost) +{ + struct cppc_perf_caps perf_caps; + u64 highest_perf, nominal_perf, perf_ratio; + int ret; + + ret = cppc_get_perf_caps(0, &perf_caps); + if (ret) { + pr_debug("Could not retrieve perf counters (%d)\n", ret); + return false; + } + + highest_perf = perf_caps.highest_perf; + nominal_perf = perf_caps.nominal_perf; + + if (!highest_perf || !nominal_perf) { + pr_debug("Could not retrieve highest or nominal performance\n"); + return false; + } + + perf_ratio = div_u64(highest_perf * SCHED_CAPACITY_SCALE, nominal_perf); + if (perf_ratio <= SCHED_CAPACITY_SCALE) { + pr_debug("Either perf_ratio is 0, or nominal >= highest performance\n"); + return false; + } + + *max_boost = max_freq * perf_ratio >> SCHED_CAPACITY_SHIFT; + + return true; +} +#else +static int amd_max_boost(unsigned int max_freq, unsigned int *max_boost) +{ + return false; +} +#endif + +DEFINE_STATIC_KEY_FALSE(cpufreq_amd_max_boost); + int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy, struct cpufreq_frequency_table *table) { struct cpufreq_frequency_table *pos; unsigned int min_freq = ~0; unsigned int max_freq = 0; + unsigned int max_boost; unsigned int freq; cpufreq_for_each_valid_entry(pos, table) { @@ -54,6 +99,12 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy, policy->min = policy->cpuinfo.min_freq = min_freq; policy->max = policy->cpuinfo.max_freq = max_freq; + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD && + amd_max_boost(max_freq, &max_boost)) { + policy->cpuinfo.max_boost = max_boost; + static_branch_enable(&cpufreq_amd_max_boost); + } + if (policy->min == ~0) return -EINVAL; else diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 9c8b7437b6cd..341cac76d254 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -40,9 +40,14 @@ enum cpufreq_table_sorting { CPUFREQ_TABLE_SORTED_DESCENDING }; +DECLARE_STATIC_KEY_FALSE(cpufreq_amd_max_boost); + +#define cpufreq_driver_has_max_boost() static_branch_unlikely(&cpufreq_amd_max_boost) + struct cpufreq_cpuinfo { unsigned int max_freq; unsigned int min_freq; + unsigned int max_boost; /* in 10^(-9) s = nanoseconds */ unsigned int transition_latency; diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 6931f0cdeb80..541f3db3f576 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -159,8 +159,12 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, unsigned long util, unsigned long max) { struct cpufreq_policy *policy = sg_policy->policy; - unsigned int freq = arch_scale_freq_invariant() ? - policy->cpuinfo.max_freq : policy->cur; + unsigned int freq, max_freq; + + max_freq = cpufreq_driver_has_max_boost() ? + policy->cpuinfo.max_boost : policy->cpuinfo.max_freq; + + freq = arch_scale_freq_invariant() ? max_freq : policy->cur; freq = map_util_freq(util, freq, max);