From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by sourceware.org (Postfix) with ESMTPS id 1BB5E3858D3C for ; Thu, 5 May 2022 02:59:43 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1BB5E3858D3C X-IronPort-AV: E=McAfee;i="6400,9594,10337"; a="249950507" X-IronPort-AV: E=Sophos;i="5.91,199,1647327600"; d="scan'208";a="249950507" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 May 2022 19:59:41 -0700 X-IronPort-AV: E=Sophos;i="5.91,199,1647327600"; d="scan'208";a="563025677" Received: from guowangy-mobl1.ccr.corp.intel.com (HELO [10.255.28.170]) ([10.255.28.170]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 May 2022 19:59:41 -0700 Message-ID: <02f7eba1-1461-6d26-3a28-958401219844@intel.com> Date: Thu, 5 May 2022 10:59:35 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v4] nptl: Add backoff mechanism to spinlock loop Content-Language: en-US To: "H.J. Lu" Cc: libc-alpha@sourceware.org References: <20220504025849.13449-1-wangyang.guo@intel.com> <20220504031710.60677-1-wangyang.guo@intel.com> From: "Guo, Wangyang" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-13.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, NICE_REPLY_A, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 05 May 2022 02:59:46 -0000 On 5/5/2022 9:56 AM, H.J. Lu via Libc-alpha wrote: > On Tue, May 3, 2022 at 8:17 PM Wangyang Guo wrote: >> >> When mutiple threads waiting for lock at the same time, once lock owner >> releases the lock, waiters will see lock available and all try to lock, >> which may cause an expensive CAS storm. >> >> Binary exponential backoff with random jitter is introduced. As try-lock >> attempt increases, there is more likely that a larger number threads >> compete for adaptive mutex lock, so increase wait time in exponential. >> A random jitter is also added to avoid synchronous try-lock from other >> threads. >> >> v2: Remove read-check before try-lock for performance. >> >> v3: >> 1. Restore read-check since it works well in some platform. >> 2. Make backoff arch dependent, and enable it for x86_64. >> 3. Limit max backoff to reduce latency in large critical section. >> >> v4: Fix strict-prototypes error in sysdeps/nptl/pthread_mutex_backoff.h >> >> Result of pthread-mutex-locks bench >> >> Test Platform: Xeon 8280L (2 socket, 112 CPUs in total) >> First Row: thread number >> First Col: critical section length >> Values: backoff vs upstream, time based, low is better >> >> non-critical-length: 1 >> 1 2 4 8 16 32 64 112 140 >> 0 0.99 0.58 0.52 0.49 0.43 0.44 0.46 0.52 0.54 >> 1 0.98 0.43 0.56 0.50 0.44 0.45 0.50 0.56 0.57 >> 2 0.99 0.41 0.57 0.51 0.45 0.47 0.48 0.60 0.61 >> 4 0.99 0.45 0.59 0.53 0.48 0.49 0.52 0.64 0.65 >> 8 1.00 0.66 0.71 0.63 0.56 0.59 0.66 0.72 0.71 >> 16 0.97 0.78 0.91 0.73 0.67 0.70 0.79 0.80 0.80 >> 32 0.95 1.17 0.98 0.87 0.82 0.86 0.89 0.90 0.90 >> 64 0.96 0.95 1.01 1.01 0.98 1.00 1.03 0.99 0.99 >> 128 0.99 1.01 1.01 1.17 1.08 1.12 1.02 0.97 1.02 >> >> non-critical-length: 32 >> 1 2 4 8 16 32 64 112 140 >> 0 1.03 0.97 0.75 0.65 0.58 0.58 0.56 0.70 0.70 >> 1 0.94 0.95 0.76 0.65 0.58 0.58 0.61 0.71 0.72 >> 2 0.97 0.96 0.77 0.66 0.58 0.59 0.62 0.74 0.74 >> 4 0.99 0.96 0.78 0.66 0.60 0.61 0.66 0.76 0.77 >> 8 0.99 0.99 0.84 0.70 0.64 0.66 0.71 0.80 0.80 >> 16 0.98 0.97 0.95 0.76 0.70 0.73 0.81 0.85 0.84 >> 32 1.04 1.12 1.04 0.89 0.82 0.86 0.93 0.91 0.91 >> 64 0.99 1.15 1.07 1.00 0.99 1.01 1.05 0.99 0.99 >> 128 1.00 1.21 1.20 1.22 1.25 1.31 1.12 1.10 0.99 >> >> non-critical-length: 128 >> 1 2 4 8 16 32 64 112 140 >> 0 1.02 1.00 0.99 0.67 0.61 0.61 0.61 0.74 0.73 >> 1 0.95 0.99 1.00 0.68 0.61 0.60 0.60 0.74 0.74 >> 2 1.00 1.04 1.00 0.68 0.59 0.61 0.65 0.76 0.76 >> 4 1.00 0.96 0.98 0.70 0.63 0.63 0.67 0.78 0.77 >> 8 1.01 1.02 0.89 0.73 0.65 0.67 0.71 0.81 0.80 >> 16 0.99 0.96 0.96 0.79 0.71 0.73 0.80 0.84 0.84 >> 32 0.99 0.95 1.05 0.89 0.84 0.85 0.94 0.92 0.91 >> 64 1.00 0.99 1.16 1.04 1.00 1.02 1.06 0.99 0.99 >> 128 1.00 1.06 0.98 1.14 1.39 1.26 1.08 1.02 0.98 > > For large critical section lengths, the new code can be up to 39% slower. > Is it true? Are small critical section lengths more common The adaptive mutex is aimed for "quick" locks. Small critical section is more common when user choose to use adaptive pthread_mutex. > >> Signed-off-by: Wangyang Guo >> --- >> nptl/pthread_mutex_lock.c | 16 +++++++-- >> sysdeps/nptl/pthreadP.h | 1 + >> sysdeps/nptl/pthread_mutex_backoff.h | 35 ++++++++++++++++++ >> sysdeps/x86_64/nptl/pthread_mutex_backoff.h | 39 +++++++++++++++++++++ >> 4 files changed, 89 insertions(+), 2 deletions(-) >> create mode 100644 sysdeps/nptl/pthread_mutex_backoff.h >> create mode 100644 sysdeps/x86_64/nptl/pthread_mutex_backoff.h >> >> diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c >> index d2e652d151..6e767a8724 100644 >> --- a/nptl/pthread_mutex_lock.c >> +++ b/nptl/pthread_mutex_lock.c >> @@ -138,14 +138,26 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) >> int cnt = 0; >> int max_cnt = MIN (max_adaptive_count (), >> mutex->__data.__spins * 2 + 10); >> + int spin_count, exp_backoff = 1; >> + unsigned int jitter = get_jitter (); >> do >> { >> - if (cnt++ >= max_cnt) >> + /* In each loop, spin count is exponential backoff plus >> + random jitter, random range is [0, exp_backoff-1]. */ >> + spin_count = exp_backoff + (jitter & (exp_backoff - 1)); >> + cnt += spin_count; >> + if (cnt >= max_cnt) >> { >> + /* If cnt exceeds max spin count, just go to wait >> + queue. */ >> LLL_MUTEX_LOCK (mutex); >> break; >> } >> - atomic_spin_nop (); >> + do >> + atomic_spin_nop (); >> + while (--spin_count > 0); >> + /* Prepare for next loop. */ >> + exp_backoff = get_next_backoff (exp_backoff); >> } >> while (LLL_MUTEX_READ_LOCK (mutex) != 0 >> || LLL_MUTEX_TRYLOCK (mutex) != 0); >> diff --git a/sysdeps/nptl/pthreadP.h b/sysdeps/nptl/pthreadP.h >> index 601db4ff2b..39af275c25 100644 >> --- a/sysdeps/nptl/pthreadP.h >> +++ b/sysdeps/nptl/pthreadP.h >> @@ -33,6 +33,7 @@ >> #include >> #include >> #include >> +#include >> #include "pthread_mutex_conf.h" >> >> >> diff --git a/sysdeps/nptl/pthread_mutex_backoff.h b/sysdeps/nptl/pthread_mutex_backoff.h >> new file mode 100644 >> index 0000000000..5b26c22ac7 >> --- /dev/null >> +++ b/sysdeps/nptl/pthread_mutex_backoff.h >> @@ -0,0 +1,35 @@ >> +/* Pthread mutex backoff configuration. >> + Copyright (C) 2022 Free Software Foundation, Inc. >> + This file is part of the GNU C Library. >> + >> + The GNU C Library is free software; you can redistribute it and/or >> + modify it under the terms of the GNU Lesser General Public >> + License as published by the Free Software Foundation; either >> + version 2.1 of the License, or (at your option) any later version. >> + >> + The GNU C Library is distributed in the hope that it will be useful, >> + but WITHOUT ANY WARRANTY; without even the implied warranty of >> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU >> + Lesser General Public License for more details. >> + >> + You should have received a copy of the GNU Lesser General Public >> + License along with the GNU C Library; if not, see >> + . */ >> +#ifndef _PTHREAD_MUTEX_BACKOFF_H >> +#define _PTHREAD_MUTEX_BACKOFF_H 1 >> + >> +static inline unsigned int >> +get_jitter (void) >> +{ >> + /* Arch dependent random jitter, return 0 disables random. */ >> + return 0; >> +} >> + >> +static inline int >> +get_next_backoff (int backoff) >> +{ >> + /* Next backoff, return 1 disables mutex backoff. */ >> + return 1; >> +} >> + >> +#endif >> diff --git a/sysdeps/x86_64/nptl/pthread_mutex_backoff.h b/sysdeps/x86_64/nptl/pthread_mutex_backoff.h >> new file mode 100644 >> index 0000000000..ec74c3d9db >> --- /dev/null >> +++ b/sysdeps/x86_64/nptl/pthread_mutex_backoff.h >> @@ -0,0 +1,39 @@ >> +/* Pthread mutex backoff configuration. >> + Copyright (C) 2022 Free Software Foundation, Inc. >> + This file is part of the GNU C Library. >> + >> + The GNU C Library is free software; you can redistribute it and/or >> + modify it under the terms of the GNU Lesser General Public >> + License as published by the Free Software Foundation; either >> + version 2.1 of the License, or (at your option) any later version. >> + >> + The GNU C Library is distributed in the hope that it will be useful, >> + but WITHOUT ANY WARRANTY; without even the implied warranty of >> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU >> + Lesser General Public License for more details. >> + >> + You should have received a copy of the GNU Lesser General Public >> + License along with the GNU C Library; if not, see >> + . */ >> +#ifndef _PTHREAD_MUTEX_BACKOFF_H >> +#define _PTHREAD_MUTEX_BACKOFF_H 1 >> + >> +#include >> + >> +static inline unsigned int >> +get_jitter (void) >> +{ >> + return get_fast_jitter (); >> +} >> + >> +#define MAX_BACKOFF 16 >> + >> +static inline int >> +get_next_backoff (int backoff) >> +{ >> + /* Binary expontial backoff. Limiting max backoff >> + can reduce latency in large critical section. */ >> + return (backoff < MAX_BACKOFF) ? backoff << 1 : backoff; >> +} >> + >> +#endif >> -- >> 2.35.1 >> > >