From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) by sourceware.org (Postfix) with ESMTPS id E574E3858400 for ; Wed, 10 Nov 2021 20:07:33 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E574E3858400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.1.2/8.16.1.2) with SMTP id 1AAJlddi004294; Wed, 10 Nov 2021 20:07:30 GMT Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 3c8mj60e2m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 10 Nov 2021 20:07:29 +0000 Received: from m0098419.ppops.net (m0098419.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.43/8.16.0.43) with SMTP id 1AAJmk1f010285; Wed, 10 Nov 2021 20:07:29 GMT Received: from ppma04dal.us.ibm.com (7a.29.35a9.ip4.static.sl-reverse.com [169.53.41.122]) by mx0b-001b2d01.pphosted.com with ESMTP id 3c8mj60e2b-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 10 Nov 2021 20:07:29 +0000 Received: from pps.filterd (ppma04dal.us.ibm.com [127.0.0.1]) by ppma04dal.us.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 1AAJvxBm007464; Wed, 10 Nov 2021 20:07:28 GMT Received: from b03cxnp08026.gho.boulder.ibm.com (b03cxnp08026.gho.boulder.ibm.com [9.17.130.18]) by ppma04dal.us.ibm.com with ESMTP id 3c5hbcgn9r-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 10 Nov 2021 20:07:28 +0000 Received: from b03ledav003.gho.boulder.ibm.com (b03ledav003.gho.boulder.ibm.com [9.17.130.234]) by b03cxnp08026.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 1AAK7Qgj54460870 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 10 Nov 2021 20:07:26 GMT Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A67DC6A069; Wed, 10 Nov 2021 20:07:26 +0000 (GMT) Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 10FEE6A05F; Wed, 10 Nov 2021 20:07:24 +0000 (GMT) Received: from li-24c3614c-2adc-11b2-a85c-85f334518bdb.ibm.com (unknown [9.65.79.57]) by b03ledav003.gho.boulder.ibm.com (Postfix) with ESMTPS; Wed, 10 Nov 2021 20:07:24 +0000 (GMT) Date: Wed, 10 Nov 2021 14:07:22 -0600 From: "Paul A. Clarke" To: Paul E Murphy Cc: "H.J. Lu" , libc-alpha@sourceware.org, Florian Weimer , Andreas Schwab , Arjan van de Ven Subject: Re: [PATCH v4 0/3] Optimize CAS [BZ #28537] Message-ID: <20211110200722.GF4930@li-24c3614c-2adc-11b2-a85c-85f334518bdb.ibm.com> References: <20211110001614.2087610-1-hjl.tools@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-TM-AS-GCONF: 00 X-Proofpoint-GUID: _fXt7rTd-rCF4-rOU4mGcXybHIK6YojD X-Proofpoint-ORIG-GUID: k0xjpQSxE2Vj0uFYOt1y90Ghw0-v8upo X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.0.607.475 definitions=2021-11-10_12,2021-11-08_02,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 adultscore=0 clxscore=1015 malwarescore=0 bulkscore=0 mlxscore=0 impostorscore=0 mlxlogscore=721 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2111100097 X-Spam-Status: No, score=-4.7 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_EF, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP 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: Wed, 10 Nov 2021 20:07:37 -0000 On Wed, Nov 10, 2021 at 08:26:09AM -0600, Paul E Murphy via Libc-alpha wrote: > On 11/9/21 6:16 PM, H.J. Lu via Libc-alpha wrote: > > CAS instruction is expensive. From the x86 CPU's point of view, getting > > a cache line for writing is more expensive than reading. See Appendix > > A.2 Spinlock in: > > > > https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/xeon-lock-scaling-analysis-paper.pdf > > > > The full compare and swap will grab the cache line exclusive and cause > > excessive cache line bouncing. > > > > Optimize CAS in low level locks and pthread_mutex_lock.c: > > > > 1. Do an atomic load and skip CAS if compare may fail to reduce cache > > line bouncing on contended locks. > > 2. Replace atomic_compare_and_exchange_bool_acq with > > atomic_compare_and_exchange_val_acq to avoid the extra load. > > 3. Drop __glibc_unlikely in __lll_trylock and lll_cond_trylock since we > > don't know if it's actually rare; in the contended case it is clearly not > > rare. > > Are you able to share benchmarks of this change? I am curious what effects > this might have on other platforms. I'd like to see the expected performance results, too. For me, the results are not uniformly positive (Power10). >From bench-pthread-locks: bench bench-patched mutex-empty 4.73371 4.54792 3.9% mutex-filler 18.5395 18.3419 1.1% mutex_trylock-empty 10.46 2.46364 76.4% mutex_trylock-filler 16.2188 16.1758 0.3% rwlock_read-empty 16.5118 16.4681 0.3% rwlock_read-filler 20.68 20.4416 1.2% rwlock_tryread-empty 2.06572 2.17284 -5.2% rwlock_tryread-filler 16.082 16.1215 -0.2% rwlock_write-empty 31.3723 31.259 0.4% rwlock_write-filler 41.6492 69.313 -66.4% rwlock_trywrite-empty 2.20584 2.32178 -5.3% rwlock_trywrite-filler 15.7044 15.9088 -1.3% spin_lock-empty 16.7964 16.7731 0.1% spin_lock-filler 20.6118 20.4175 0.9% spin_trylock-empty 8.99989 8.98879 0.1% spin_trylock-filler 16.4732 15.9957 2.9% sem_wait-empty 15.805 15.7391 0.4% sem_wait-filler 19.2346 19.5098 -1.4% sem_trywait-empty 2.06405 2.03782 1.3% sem_trywait-filler 15.921 15.8408 0.5% condvar-empty 1385.84 1387.29 -0.1% condvar-filler 1419.82 1424.01 -0.3% consumer_producer-empty 2550.01 2395.29 6.1% consumer_producer-filler 2709.4 2558.28 5.6% PC