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X-CSE-ConnectionGUID: Vr3+rJB0TV2UEEgWF/Q7Gg== X-CSE-MsgGUID: j91WizMzSRCkyklHbAk7sQ== X-IronPort-AV: E=McAfee;i="6700,10204,11222"; a="53484808" X-IronPort-AV: E=Sophos;i="6.11,196,1725346800"; d="scan'208";a="53484808" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Oct 2024 10:44:37 -0700 X-CSE-ConnectionGUID: PZ0nGUhFSMSVDp5VOS6Hjg== X-CSE-MsgGUID: BdzFP1/TTO2mjsNMiikvVA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,196,1725346800"; d="scan'208";a="77176048" Received: from rchatre-mobl4.amr.corp.intel.com (HELO [10.125.111.159]) ([10.125.111.159]) by orviesa006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Oct 2024 10:44:36 -0700 Message-ID: <0069d2dd01235b8e301837b041c4db58b296fbab.camel@linux.intel.com> Subject: Re: [PATCH v6] perf sched timehist: Add pre-migration wait time option From: Tim Chen To: Namhyung Kim , Madadi Vineeth Reddy Cc: Arnaldo Carvalho de Melo , Ian Rogers , Athira Rajeev , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Adrian Hunter , Kan Liang , acme@redhat.com, linux-perf-users , LKML Date: Fri, 11 Oct 2024 10:44:35 -0700 In-Reply-To: References: <20241004170756.18064-1-vineethr@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 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2024-10-10 at 09:23 -0700, Namhyung Kim wrote: > Hello Tim, >=20 > On Fri, Oct 04, 2024 at 10:37:56PM +0530, Madadi Vineeth Reddy wrote: > > pre-migration wait time is the time that a task unnecessarily spends > > on the runqueue of a CPU but doesn't get switched-in there. In terms > > of tracepoints, it is the time between sched:sched_wakeup and > > sched:sched_migrate_task. > >=20 > > Let's say a task woke up on CPU2, then it got migrated to CPU4 and > > then it's switched-in to CPU4. So, here pre-migration wait time is > > time that it was waiting on runqueue of CPU2 after it is woken up. > >=20 > > The general pattern for pre-migration to occur is: > > sched:sched_wakeup > > sched:sched_migrate_task > > sched:sched_switch > >=20 > > The sched:sched_waking event is used to capture the wakeup time, > > as it aligns with the existing code and only introduces a negligible > > time difference. > >=20 > > pre-migrations are generally not useful and it increases migrations. > > This metric would be helpful in testing patches mainly related to wakeu= p > > and load-balancer code paths as better wakeup logic would choose an > > optimal CPU where task would be switched-in and thereby reducing pre- > > migrations. > >=20 > > The sample output(s) when -P or --pre-migrations is used: > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > time cpu task name wait time sch = delay run time pre-mig time > > [tid/pid] (msec) (= msec) (msec) (msec) > > --------------- ------ ------------------------------ --------- ----= ----- --------- --------- > > 38456.720806 [0001] schbench[28634/28574] 4.917 = 4.768 1.004 0.000 > > 38456.720810 [0001] rcu_preempt[18] 3.919 = 0.003 0.004 0.000 > > 38456.721800 [0006] schbench[28779/28574] 23.465 2= 3.465 1.999 0.000 > > 38456.722800 [0002] schbench[28773/28574] 60.371 6= 0.237 3.955 60.197 > > 38456.722806 [0001] schbench[28634/28574] 0.004 = 0.004 1.996 0.000 > > 38456.722811 [0001] rcu_preempt[18] 1.996 = 0.005 0.005 0.000 > > 38456.723800 [0000] schbench[28833/28574] 4.000 = 4.000 3.999 0.000 > > 38456.723800 [0004] schbench[28762/28574] 42.951 4= 2.839 3.999 39.867 > > 38456.723802 [0007] schbench[28812/28574] 43.947 4= 3.817 3.999 40.866 > > 38456.723804 [0001] schbench[28587/28574] 7.935 = 7.822 0.993 0.000 > >=20 > > Signed-off-by: Madadi Vineeth Reddy > >=20 > > --- > > Changes in v6: > > - Handle the case of multiple migrations before the task is > > scheduled in. (Tim Chen) >=20 > Are you ok with this now? Yes, you can add my reviewed-by. >=20 > Thanks, > Namhyung >=20 >=20