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X-CSE-ConnectionGUID: G6VI/g9qRi+HRr31Rgqd6w== X-CSE-MsgGUID: +v7SpQHCSS2GPD6x7rd9xg== X-IronPort-AV: E=McAfee;i="6800,10657,11609"; a="68497487" X-IronPort-AV: E=Sophos;i="6.19,294,1754982000"; d="scan'208";a="68497487" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Nov 2025 10:19:19 -0800 X-CSE-ConnectionGUID: YLVQ2DaOT3W6AZX5iu94Xg== X-CSE-MsgGUID: g6rSbShESvOSQMy/Zk8lSA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,294,1754982000"; d="scan'208";a="193926148" Received: from unknown (HELO [10.241.243.18]) ([10.241.243.18]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Nov 2025 10:19:18 -0800 Message-ID: <8e47ec72494ba67a4da3c86aeebfb80908d98f40.camel@linux.intel.com> Subject: Re: [PATCH v3] sched/fair: Skip sched_balance_running cmpxchg when balance is not due From: Tim Chen To: K Prateek Nayak , Shrikanth Hegde , Peter Zijlstra Cc: Ingo Molnar , Chen Yu , Doug Nelson , Mohini Narkhede , linux-kernel@vger.kernel.org, Vincent Guittot Date: Mon, 10 Nov 2025 10:19:18 -0800 In-Reply-To: References: <52fcd1e8582a6b014a70f0ce7795ce0d88cd63a8.1762470554.git.tim.c.chen@linux.intel.com> <1d6c22aa-c882-4833-b0be-a3999d684885@amd.com> <2edf1a85-4736-4e8b-bfc9-003dd1f34be7@linux.ibm.com> Autocrypt: addr=tim.c.chen@linux.intel.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-11-10 at 09:28 +0530, K Prateek Nayak wrote: > Hello Shrikanth, >=20 > On 11/7/2025 2:27 PM, Shrikanth Hegde wrote: > > > > =C2=A0 @@ -11768,6 +11784,13 @@ static int sched_balance_rq(int thi= s_cpu, struct rq *this_rq, > > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto out_bal= anced; > > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } > > > > =C2=A0 +=C2=A0=C2=A0=C2=A0 if (idle !=3D CPU_NEWLY_IDLE && (sd->fla= gs & SD_SERIALIZE)) { > >=20 > > Can you also try removing "idle !=3D CPU_NEWLY_IDLE" and see the worklo= ad behavior? > > If workloads don't observe regression, it might be worth serializing it= too. >=20 > P.S. In one of my previous testing, I had tested only serialized for > !env.idle (__CPU_NOT_IDLE) and I didn't spot any difference in my > benchmark runs compared to always serializing. >=20 > I believe the "max_newidle_lb_cost" along with the plethora of > need_resched() checks we have help bail out of newidle balance if > there is a wakeup on the same CPU. >=20 > Idle balance too was okay with a greater number of search. If the > first CPU of group fails to pull any task and remains idle, all > the other idle CPUs simply bail out at should_we_balance() which > is probably why there was no difference in the set of benchmarks I > tested. >=20 > Serializing all shouldn't make it any worse that what we have now > so I don't mind either. Serializing the CPU_NEWLY_IDLE case does not make things worse from our testing. I will be posting an updated patch shortly. Tim