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[2620:137:e000::1:20]) by mx.google.com with ESMTP id y191-20020a638ac8000000b0040ce2432b6csi13212106pgd.586.2022.06.27.07.39.42; Mon, 27 Jun 2022 07:39:57 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237475AbiF0O15 (ORCPT + 99 others); Mon, 27 Jun 2022 10:27:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237570AbiF0O1s (ORCPT ); Mon, 27 Jun 2022 10:27:48 -0400 Received: from smtpproxy21.qq.com (smtpbg701.qq.com [203.205.195.86]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B5A5E13F28 for ; Mon, 27 Jun 2022 07:27:46 -0700 (PDT) X-QQ-mid: bizesmtp75t1656340056t09cedwu Received: from localhost.localdomain ( [113.200.76.118]) by bizesmtp.qq.com (ESMTP) with id ; Mon, 27 Jun 2022 22:27:34 +0800 (CST) X-QQ-SSF: 01400000002000D0F000C00A0000000 X-QQ-FEAT: Mzskoac49OhQU500IjO78DhojBQSVQY5LrRe4VDr5T3QMGZTvCJrn2JUWeURT bcfoOes4gEgommRY4shN8o4bfMVaFeRUnv2c2vWOknpSQyUr3FUGVKzUtQaKX4n/zaAyGWI jBOgr9cEhmneAgOq/m76lJtsH+GAOdZ0LUfz6/215PZlGHfkI88jDjE6j+g04zriUkbqQhE lMmmr2RQk9inCQefZ1xQwcQ3ZDYKTR54K9cjLuK9yQx/7oEpJBgGZtAr6IvUPvcrzhPCRkS TC5mArahUCJqTadSIzaqd9Sq3x0A/Zh/ZPTjj78oI7thYgjykkSbAPoYxnOw3xID+jnJp1I IlFRM2TOwBixHobAmlgQdG2T3/+eqzle9pKzd7g X-QQ-GoodBg: 2 From: Guo Hui To: peterz@infradead.org Cc: longman@redhat.com, jgross@suse.com, srivatsa@csail.mit.edu, amakhalov@vmware.com, pv-drivers@vmware.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, will@kernel.org, boqun.feng@gmail.com, virtualization@lists.linux-foundation.org, wangxiaohua@uniontech.com, linux-kernel@vger.kernel.org, Guo Hui Subject: [PATCH v4] x86/paravirt: useless assignment instructions cause Unixbench full core performance degradation Date: Mon, 27 Jun 2022 22:27:32 +0800 Message-Id: <20220627142732.31067-1-guohui@uniontech.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:uniontech.com:qybgforeign:qybgforeign3 X-QQ-Bgrelay: 1 X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_NONE, SPF_HELO_PASS,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The instructions assigned to the vcpu_is_preempted function parameter in the X86 architecture physical machine are redundant instructions, causing the multi-core performance of Unixbench to drop by about 4% to 5%. The C function is as follows: static bool vcpu_is_preempted(long vcpu); The parameter 'vcpu' in the function osq_lock that calls the function vcpu_is_preempted is assigned as follows: The C code is in the function node_cpu: cpu = node->cpu - 1; The instructions corresponding to the C code are: mov 0x14(%rax),%edi sub $0x1,%edi The above instructions are unnecessary in the X86 Native operating environment, causing high cache-misses and degrading performance. This patch uses static_key to not execute this instruction in the Native runtime environment. The patch effect is as follows two machines, Unixbench runs with full core score: 1. Machine configuration: Intel(R) Xeon(R) Silver 4210 CPU @ 2.20GHz CPU core: 40 Memory: 256G OS Kernel: 5.19-rc3 Before using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 948326591.2 81261.9 Double-Precision Whetstone 55.0 211986.3 38543.0 Execl Throughput 43.0 43453.2 10105.4 File Copy 1024 bufsize 2000 maxblocks 3960.0 438936.2 1108.4 File Copy 256 bufsize 500 maxblocks 1655.0 118197.4 714.2 File Copy 4096 bufsize 8000 maxblocks 5800.0 1534674.7 2646.0 Pipe Throughput 12440.0 46482107.6 37365.0 Pipe-based Context Switching 4000.0 1915094.2 4787.7 Process Creation 126.0 85442.2 6781.1 Shell Scripts (1 concurrent) 42.4 69400.7 16368.1 Shell Scripts (8 concurrent) 6.0 8877.2 14795.3 System Call Overhead 15000.0 4714906.1 3143.3 ======== System Benchmarks Index Score 7923.3 After using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 947032915.5 81151.1 Double-Precision Whetstone 55.0 211971.2 38540.2 Execl Throughput 43.0 45054.8 10477.9 File Copy 1024 bufsize 2000 maxblocks 3960.0 515024.9 1300.6 File Copy 256 bufsize 500 maxblocks 1655.0 146354.6 884.3 File Copy 4096 bufsize 8000 maxblocks 5800.0 1679995.9 2896.5 Pipe Throughput 12440.0 46466394.2 37352.4 Pipe-based Context Switching 4000.0 1898221.4 4745.6 Process Creation 126.0 85653.1 6797.9 Shell Scripts (1 concurrent) 42.4 69437.3 16376.7 Shell Scripts (8 concurrent) 6.0 8898.9 14831.4 System Call Overhead 15000.0 4658746.7 3105.8 ======== System Benchmarks Index Score 8248.8 2. Machine configuration: Hygon C86 7185 32-core Processor CPU core: 128 Memory: 256G OS Kernel: 5.19-rc3 Before using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 2256644068.3 193371.4 Double-Precision Whetstone 55.0 438969.9 79812.7 Execl Throughput 43.0 10108.6 2350.8 File Copy 1024 bufsize 2000 maxblocks 3960.0 275892.8 696.7 File Copy 256 bufsize 500 maxblocks 1655.0 72082.7 435.5 File Copy 4096 bufsize 8000 maxblocks 5800.0 925043.4 1594.9 Pipe Throughput 12440.0 118905512.5 95583.2 Pipe-based Context Switching 4000.0 7820945.7 19552.4 Process Creation 126.0 31233.3 2478.8 Shell Scripts (1 concurrent) 42.4 49042.8 11566.7 Shell Scripts (8 concurrent) 6.0 6656.0 11093.3 System Call Overhead 15000.0 6816047.5 4544.0 ======== System Benchmarks Index Score 7756.6 After using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 2252272929.4 192996.8 Double-Precision Whetstone 55.0 451847.2 82154.0 Execl Throughput 43.0 10595.1 2464.0 File Copy 1024 bufsize 2000 maxblocks 3960.0 301279.3 760.8 File Copy 256 bufsize 500 maxblocks 1655.0 79291.3 479.1 File Copy 4096 bufsize 8000 maxblocks 5800.0 1039755.2 1792.7 Pipe Throughput 12440.0 118701468.1 95419.2 Pipe-based Context Switching 4000.0 8073453.3 20183.6 Process Creation 126.0 33440.9 2654.0 Shell Scripts (1 concurrent) 42.4 52722.6 12434.6 Shell Scripts (8 concurrent) 6.0 7050.4 11750.6 System Call Overhead 15000.0 6834371.5 4556.2 ======== System Benchmarks Index Score 8157.8 Signed-off-by: Guo Hui --- arch/x86/kernel/paravirt-spinlocks.c | 4 ++++ kernel/locking/osq_lock.c | 12 +++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c index 9e1ea99ad..a2eb375e2 100644 --- a/arch/x86/kernel/paravirt-spinlocks.c +++ b/arch/x86/kernel/paravirt-spinlocks.c @@ -33,6 +33,8 @@ bool pv_is_native_vcpu_is_preempted(void) __raw_callee_save___native_vcpu_is_preempted; } +DECLARE_STATIC_KEY_TRUE(vcpu_has_preemption); + void __init paravirt_set_cap(void) { if (!pv_is_native_spin_unlock()) @@ -40,4 +42,6 @@ void __init paravirt_set_cap(void) if (!pv_is_native_vcpu_is_preempted()) setup_force_cpu_cap(X86_FEATURE_VCPUPREEMPT); + else + static_branch_disable(&vcpu_has_preemption); } diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index d5610ad52..adb41080d 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -27,6 +27,16 @@ static inline int node_cpu(struct optimistic_spin_node *node) return node->cpu - 1; } +DEFINE_STATIC_KEY_TRUE(vcpu_has_preemption); + +static inline bool vcpu_is_preempted_node(struct optimistic_spin_node *node) +{ + if (!static_branch_unlikely(&vcpu_has_preemption)) + return false; + + return vcpu_is_preempted(node_cpu(node->prev)); +} + static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) { int cpu_nr = encoded_cpu_val - 1; @@ -141,7 +151,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) * polling, be careful. */ if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() || - vcpu_is_preempted(node_cpu(node->prev)))) + vcpu_is_preempted_node(node))) return true; /* unqueue */ -- 2.20.1