Re: [RFD] resctrl: reassigning a running container's CTRL_MON group

From: Peter Newman <peternewman@google.com>
To: Reinette Chatre <reinette.chatre@intel.com>
Cc: James Morse <james.morse@arm.com>,
	Tony Luck <tony.luck@intel.com>,
	"Yu, Fenghua" <fenghua.yu@intel.com>,
	"Eranian, Stephane" <eranian@google.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Babu Moger <Babu.Moger@amd.com>,
	Gaurang Upasani <gupasani@google.com>
Subject: Re: [RFD] resctrl: reassigning a running container's CTRL_MON group
Date: Tue, 1 Nov 2022 16:53:12 +0100	[thread overview]
Message-ID: <CALPaoCikWKz8VLf5QdeYm5k58tePTpb3nTKMGJ+qeGmevjvMpg@mail.gmail.com> (raw)
In-Reply-To: <CALPaoCj8bVo3Z1r9_Ag=6KvGuR2wzQesArwZKEDvudGPYbbwaA@mail.gmail.com>

On Tue, Nov 1, 2022 at 4:23 PM Peter Newman <peternewman@google.com> wrote:
> Yes it looks like the task's rq_lock would provide the necessary
> ordering. It's not feasible to ensure the IPI arrives before the target
> task migrates away, but the task would need to obtain the same lock in
> order to migrate off of its current CPU, so that alone would ensure the
> next migration would observe the updates.
>
> The difficulty is this lock is private to sched/, so I'd have to propose
> some API.

Actually it looks like I can just use task_call_func() to lock down the
task while we do our updates and decide if or where to send IPIs. That
seems easy enough.

-Peter