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 AA631C43334 for ; Mon, 27 Jun 2022 02:14:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231438AbiF0COT (ORCPT ); Sun, 26 Jun 2022 22:14:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44512 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229867AbiF0COR (ORCPT ); Sun, 26 Jun 2022 22:14:17 -0400 Received: from qq.com (smtpbg465.qq.com [59.36.132.35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 763DE270C for ; Sun, 26 Jun 2022 19:14:15 -0700 (PDT) X-QQ-mid: bizesmtp75t1656296035txn2x220 Received: from localhost.localdomain ( [113.200.76.118]) by bizesmtp.qq.com (ESMTP) with id ; Mon, 27 Jun 2022 10:13:53 +0800 (CST) X-QQ-SSF: 01400000000000C0F000000A0000000 X-QQ-FEAT: GFUnPs55yMXjhB9hu27UN/jjlpzlI15WzDmJXWxLSBWfAZqXNHLVgi1cpSHEy oPilcCSLTj3Cl9x3k0jpd1p8sp5iloeNqiZj6bpm/TShaXpx0UZEr2/ytpoHxWg0uldij4A z172FAWNDw9lWvzVvjNIfY93hsL2XrtN4/9/zZ75FCDujyL63q3XwwS9UWaJMjqxZdH4CBo u3dMEVFm7YGP4vpN+cDm4UjGgmZqUVjbhwj2aRnZH+40qE/gngtu3xGotyHBxGpl2quGEP8 lv/Th6YHQqaPMkYZ9ovZxtWdTqNvwz8+n7ha1p/MqFeWHWjZYTpv2/8KguMXA9nE6DgvIYW WKq303nM76pgMGhH24GagyOiGolv/Mwwz/mWnQV X-QQ-GoodBg: 1 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 v2] x86/paravirt: useless assignment instructions cause Unixbench full core performance degradation Date: Mon, 27 Jun 2022 10:13:50 +0800 Message-Id: <20220627021350.25714-1-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:qybgforeign9 X-QQ-Bgrelay: 1 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 code is as follows: DEFINE_STATIC_KEY_FALSE(preemted_key); static inline int node_cpu(struct optimistic_spin_node *node) { int cpu = 0; if (!static_branch_unlikely(&preemted_key)) cpu = node->cpu - 1; return cpu; } 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 | 9 ++++++++- 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c index 9e1ea99ad..7a55f8407 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_FALSE(preemted_key); + 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_enable(&preemted_key); } diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index d5610ad52..a8798e701 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -22,9 +22,16 @@ static inline int encode_cpu(int cpu_nr) return cpu_nr + 1; } +DEFINE_STATIC_KEY_FALSE(preemted_key); + static inline int node_cpu(struct optimistic_spin_node *node) { - return node->cpu - 1; + int cpu = 0; + + if (!static_branch_unlikely(&preemted_key)) + cpu = node->cpu - 1; + + return cpu; } static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) -- 2.20.1