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Mon, 5 Jan 2026 03:53:18 +0000 Received: from satlexmb07.amd.com (10.181.42.216) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Sun, 4 Jan 2026 21:53:07 -0600 Received: from [10.136.46.19] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Sun, 4 Jan 2026 19:53:04 -0800 Message-ID: Date: Mon, 5 Jan 2026 09:22:58 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] sched/fair: Change likelyhood of nohz.nr_cpus and do stats update if its due To: Shrikanth Hegde , , , CC: , , , , , , , References: <20260102124744.360872-1-sshegde@linux.ibm.com> <20260102124744.360872-3-sshegde@linux.ibm.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20260102124744.360872-3-sshegde@linux.ibm.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Jan 2026 03:53:18.2192 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1037ae9e-dcfe-4316-f3c0-08de4c0df63b X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN2PEPF0000449E.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR12MB4430 Hello Shrikanth, On 1/2/2026 6:17 PM, Shrikanth Hegde wrote: > These days most of the system have multi cores. The likelyhood of > at least one or more CPUs in nohz (idle state) is higher. > So move likely to unlikely. > > Allow stats balancing to complete when there are no nr_cpus as the check > happens later. This may do an additional stats based load balancing > which would reset has_blocked_load. Code also looks saner by removing > that uncharactiristic return in between. > > Signed-off-by: Shrikanth Hegde > --- > kernel/sched/fair.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index cd1c78d2c272..5ceb9126d441 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -12456,10 +12456,10 @@ static void nohz_balancer_kick(struct rq *rq) > > /* > * None are in tickless mode and hence no need for NOHZ idle load > - * balancing: > + * balancing, do stats update if its due > */ > - if (likely(!atomic_read(&nohz.nr_cpus))) > - return; > + if (unlikely(!atomic_read(&nohz.nohz_balancer_kick))) > + goto out; Since we are sure that "nohz.nr_cpus" is 0, there is a good chance find_new_ilb() in kick_ilb() will not find any CPU to run balance on, so why not just retain that return? The "flags" can only be set to (NOHZ_NEXT_KICK | NOHZ_STATS_KICK) on this path and kick_ilb() will simply return early without updating "nohz.next_balance" when it doesn't see NOHZ_BALANCE_KICK and fails to find any CPU. Might as well keep the early return. > > if (rq->nr_running >= 2) { > flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; -- Thanks and Regards, Prateek