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Fri, 1 Mar 2024 15:35:09 GMT Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 35D6958061; Fri, 1 Mar 2024 15:35:07 +0000 (GMT) Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 448AC58068; Fri, 1 Mar 2024 15:35:04 +0000 (GMT) Received: from [9.43.59.36] (unknown [9.43.59.36]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTP; Fri, 1 Mar 2024 15:35:03 +0000 (GMT) Message-ID: <703aad5f-40ce-4b37-bd5d-4a85615085e4@linux.ibm.com> Date: Fri, 1 Mar 2024 21:05:02 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/7] sched/balancing: Switch the 'DEFINE_SPINLOCK(balancing)' spinlock into an 'atomic_t sched_balance_running' flag Content-Language: en-US To: Ingo Molnar Cc: Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Linus Torvalds , Valentin Schneider , Nicholas Piggin , LKML References: <20240301110951.3707367-1-mingo@kernel.org> <20240301110951.3707367-2-mingo@kernel.org> From: Shrikanth Hegde In-Reply-To: <20240301110951.3707367-2-mingo@kernel.org> Content-Type: text/plain; charset=UTF-8 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: _6QaWMMlsIR-KJ6SQtkoxDX_75FXiC5b X-Proofpoint-ORIG-GUID: iI-mhrJtOD3w5KAJ_Q9nCWruUGndZcMw Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-03-01_14,2024-03-01_02,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 clxscore=1011 malwarescore=0 priorityscore=1501 mlxscore=0 suspectscore=0 mlxlogscore=707 adultscore=0 phishscore=0 impostorscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2403010129 On 3/1/24 4:39 PM, Ingo Molnar wrote: > The 'balancing' spinlock added in: Hi Ingo. > > 08c183f31bdb ("[PATCH] sched: add option to serialize load balancing") > [...] > > need_serialize = sd->flags & SD_SERIALIZE; > if (need_serialize) { > - if (!spin_trylock(&balancing)) > + if (atomic_cmpxchg_acquire(&sched_balance_running, 0, 1)) Thinking from very little I know, I may be completely wrong. Is it possible that arch_spin_trylock, which would be called from spin_trylock is faster in some architectures? Maybe in contended case? For example, in powerpc, queued_spin_trylock, uses more optimal ll/sc style access patterns rather than cmpxchg. https://lore.kernel.org/all/20221126095932.1234527-4-npiggin@gmail.com/ +nick > goto out; > } > > @@ -11729,7 +11742,7 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle) > interval = get_sd_balance_interval(sd, busy); > } > if (need_serialize) > - spin_unlock(&balancing); > + atomic_set_release(&sched_balance_running, 0); > out: > if (time_after(next_balance, sd->last_balance + interval)) { > next_balance = sd->last_balance + interval;