From nobody Sun Feb 8 17:37:29 2026 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 72383C7EE29 for ; Tue, 23 May 2023 08:51:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236021AbjEWIvZ (ORCPT ); Tue, 23 May 2023 04:51:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230487AbjEWIvX (ORCPT ); Tue, 23 May 2023 04:51:23 -0400 Received: from mail-pf1-x430.google.com (mail-pf1-x430.google.com [IPv6:2607:f8b0:4864:20::430]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4D80C95; Tue, 23 May 2023 01:51:22 -0700 (PDT) Received: by mail-pf1-x430.google.com with SMTP id d2e1a72fcca58-64d44b198baso2296672b3a.0; Tue, 23 May 2023 01:51:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1684831882; x=1687423882; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=Vd9VcsDJ8elNncryM1wYDU//sBkMxzd/B1cmsfb/p9A=; b=KRfyQ2yxg+B7sqQkFqe1Icwkw7vdlDlF4Jjm18E2uU/CLmX3WGaWEIal3LtT87uU3L YINOR4HoEE0OHEq6xiRw7CX3WGxnjr5t8vqR5jEXtL0C6uVg+gHJQHm/qZw2pUrwU+Fv HbgB3fy4g/axMQFx50hIFJi96+sfyb310fOumH7g1iaSQ44+hAAQHcRlo0O7uCMWFln1 /MX5oaccf6cTe9aI2IVfTWTncK6f29rODp0zmbjgbTPX/zfKWJzBqwJ4zN96rsB/9Mg4 Cs1RRVmqHCjxxExJOMty8JQp3uGr8yBIsFUqinpKOu8mjTgkoBjQfX6X6IT7n4J9xyH3 3lcA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1684831882; x=1687423882; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=Vd9VcsDJ8elNncryM1wYDU//sBkMxzd/B1cmsfb/p9A=; b=HP+vu6S54ZdXwWuPno4mrPeKcsD8VKycLyh3e9aX5hseb7JBkb+8JokSRrCjYBXzsV NbRTfB7ibPGMo6B8LO26k50veOVehULyYOgdLhWkefrguvzA+GTeQO4A7S1NFatOcjda mByTOFE/L+tf9FtPX4i/MB92wys5eULU/rdlU4iCyWg5CaDGJryiZ9SRpY+hXcPpzZ09 rTDXxDPnYIDlEpSvBrj5AimjdoKCTQH3Ry3QL+Y2Qq9v54fY3byCbIyVnxPlxg0rdqC3 ZZH9harVjYGI5nHcpdeAFCn5JB2Dtb7WZU9lq87T+5JlX6XRj9zxL+NSbu1SR20kJGAD 9/Pw== X-Gm-Message-State: AC+VfDyKiBeJdcpBQjJjByrxtgCnh0Zi9ckIkEeUo1kxegDtwMKb9Dsa ey4QR6DqCd9+Z3ddG6dLA5t4ofOuiYEKQA== X-Google-Smtp-Source: ACHHUZ6YH8rNBdpo5UrIZanYvNELj214VsoUYf3zvSmBtNnTx4OfnO3JhnekIwU2fCxyUD17miL9xw== X-Received: by 2002:a05:6a00:806:b0:64f:3840:3c24 with SMTP id m6-20020a056a00080600b0064f38403c24mr2313324pfk.16.1684831881574; Tue, 23 May 2023 01:51:21 -0700 (PDT) Received: from localhost.localdomain ([202.160.36.160]) by smtp.googlemail.com with ESMTPSA id l15-20020a62be0f000000b0064d57ecaa1dsm786417pff.28.2023.05.23.01.51.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 May 2023 01:51:20 -0700 (PDT) From: Fieah Lim To: srinivas.pandruvada@linux.intel.com, lenb@kernel.org, rafael@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Fieah Lim Subject: [PATCH v2] cpufreq: intel_pstate: Avoid initializing variables prematurely Date: Tue, 23 May 2023 16:50:45 +0800 Message-Id: <20230523085045.29391-1-kweifat@gmail.com> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" We should avoid initializing some rather expensive data when the function has a chance to bail out earlier before actually using it. This applies to the following initializations: - cpudata *cpu =3D all_cpu_data; (in everywhere) - this_cpu =3D smp_processor_id(); (in notify_hwp_interrupt) - hwp_cap =3D READ_ONCE(cpu->hwp_cap_cached); (in intel_pstate_hwp_boost_u= p) These initializations are premature because there is a chance that the function will bail out before actually using the data. I think this qualifies as a micro-optimization, especially in such a hot path. While at it, tidy up how and when we initialize all of the cpu_data pointers, for the sake of consistency. A side note on the intel_pstate_cpu_online change: we simply don't have to initialize cpudata just for the pr_debug, while policy->cpu is being there. Signed-off-by: Fieah Lim --- V1 -> V2: Rewrite changelog for better explanation. --- drivers/cpufreq/intel_pstate.c | 35 +++++++++++++++++++--------------- 1 file changed, 20 insertions(+), 15 deletions(-) diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 2548ec92faa2..b85e340520d9 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -464,9 +464,8 @@ static void intel_pstate_init_acpi_perf_limits(struct c= pufreq_policy *policy) =20 static void intel_pstate_exit_perf_limits(struct cpufreq_policy *policy) { - struct cpudata *cpu; + struct cpudata *cpu =3D all_cpu_data[policy->cpu]; =20 - cpu =3D all_cpu_data[policy->cpu]; if (!cpu->valid_pss_table) return; =20 @@ -539,9 +538,8 @@ static void intel_pstate_hybrid_hwp_adjust(struct cpuda= ta *cpu) static inline void update_turbo_state(void) { u64 misc_en; - struct cpudata *cpu; + struct cpudata *cpu =3D all_cpu_data[0]; =20 - cpu =3D all_cpu_data[0]; rdmsrl(MSR_IA32_MISC_ENABLE, misc_en); global.turbo_disabled =3D (misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE || @@ -769,7 +767,7 @@ static struct cpufreq_driver intel_pstate; static ssize_t store_energy_performance_preference( struct cpufreq_policy *policy, const char *buf, size_t count) { - struct cpudata *cpu =3D all_cpu_data[policy->cpu]; + struct cpudata *cpu; char str_preference[21]; bool raw =3D false; ssize_t ret; @@ -802,6 +800,8 @@ static ssize_t store_energy_performance_preference( if (!intel_pstate_driver) return -EAGAIN; =20 + cpu =3D all_cpu_data[policy->cpu]; + mutex_lock(&intel_pstate_limits_lock); =20 if (intel_pstate_driver =3D=3D &intel_pstate) { @@ -1297,7 +1297,7 @@ static void update_qos_request(enum freq_qos_req_type= type) int i; =20 for_each_possible_cpu(i) { - struct cpudata *cpu =3D all_cpu_data[i]; + struct cpudata *cpu; unsigned int freq, perf_pct; =20 policy =3D cpufreq_cpu_get(i); @@ -1310,6 +1310,8 @@ static void update_qos_request(enum freq_qos_req_type= type) if (!req) continue; =20 + cpu =3D all_cpu_data[i]; + if (hwp_active) intel_pstate_get_hwp_cap(cpu); =20 @@ -1579,7 +1581,7 @@ static cpumask_t hwp_intr_enable_mask; =20 void notify_hwp_interrupt(void) { - unsigned int this_cpu =3D smp_processor_id(); + unsigned int this_cpu; struct cpudata *cpudata; unsigned long flags; u64 value; @@ -1591,6 +1593,8 @@ void notify_hwp_interrupt(void) if (!(value & 0x01)) return; =20 + this_cpu =3D smp_processor_id(); + spin_lock_irqsave(&hwp_notify_lock, flags); =20 if (!cpumask_test_cpu(this_cpu, &hwp_intr_enable_mask)) @@ -2024,8 +2028,8 @@ static int hwp_boost_hold_time_ns =3D 3 * NSEC_PER_MS= EC; =20 static inline void intel_pstate_hwp_boost_up(struct cpudata *cpu) { + u64 hwp_cap; u64 hwp_req =3D READ_ONCE(cpu->hwp_req_cached); - u64 hwp_cap =3D READ_ONCE(cpu->hwp_cap_cached); u32 max_limit =3D (hwp_req & 0xff00) >> 8; u32 min_limit =3D (hwp_req & 0xff); u32 boost_level1; @@ -2052,6 +2056,7 @@ static inline void intel_pstate_hwp_boost_up(struct c= pudata *cpu) cpu->hwp_boost_min =3D min_limit; =20 /* level at half way mark between min and guranteed */ + hwp_cap =3D READ_ONCE(cpu->hwp_cap_cached); boost_level1 =3D (HWP_GUARANTEED_PERF(hwp_cap) + min_limit) >> 1; =20 if (cpu->hwp_boost_min < boost_level1) @@ -2389,9 +2394,7 @@ static const struct x86_cpu_id intel_pstate_cpu_ee_di= sable_ids[] =3D { =20 static int intel_pstate_init_cpu(unsigned int cpunum) { - struct cpudata *cpu; - - cpu =3D all_cpu_data[cpunum]; + struct cpudata *cpu =3D all_cpu_data[cpunum]; =20 if (!cpu) { cpu =3D kzalloc(sizeof(*cpu), GFP_KERNEL); @@ -2431,11 +2434,13 @@ static int intel_pstate_init_cpu(unsigned int cpunu= m) =20 static void intel_pstate_set_update_util_hook(unsigned int cpu_num) { - struct cpudata *cpu =3D all_cpu_data[cpu_num]; + struct cpudata *cpu; =20 if (hwp_active && !hwp_boost) return; =20 + cpu =3D all_cpu_data[cpu_num]; + if (cpu->update_util_set) return; =20 @@ -2638,9 +2643,7 @@ static int intel_cpufreq_cpu_offline(struct cpufreq_p= olicy *policy) =20 static int intel_pstate_cpu_online(struct cpufreq_policy *policy) { - struct cpudata *cpu =3D all_cpu_data[policy->cpu]; - - pr_debug("CPU %d going online\n", cpu->cpu); + pr_debug("CPU %d going online\n", policy->cpu); =20 intel_pstate_init_acpi_perf_limits(policy); =20 @@ -2649,6 +2652,8 @@ static int intel_pstate_cpu_online(struct cpufreq_pol= icy *policy) * Re-enable HWP and clear the "suspended" flag to let "resume" * know that it need not do that. */ + struct cpudata *cpu =3D all_cpu_data[policy->cpu]; + intel_pstate_hwp_reenable(cpu); cpu->suspended =3D false; } --=20 2.40.1