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Message-ID: <CALPaoChNAaoJ7uzuxFFDn-f5nvUCXyJ4jkbETHXNdDpXNnh9pQ@mail.gmail.com>
Date: Thu, 27 Oct 2022 09:56:33 +0200
From: Peter Newman <peternewman@...gle.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: James Morse <james.morse@....com>, Tony Luck <tony.luck@...el.com>,
"Yu, Fenghua" <fenghua.yu@...el.com>,
"Eranian, Stephane" <eranian@...gle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Babu Moger <Babu.Moger@....com>,
Gaurang Upasani <gupasani@...gle.com>
Subject: Re: [RFD] resctrl: reassigning a running container's CTRL_MON group
Hi Reinette,
On Wed, Oct 26, 2022 at 11:12 PM Reinette Chatre
<reinette.chatre@...el.com> wrote:
> The original concern is "the stores to t->closid and t->rmid could be
> reordered with the task_curr(t) and task_cpu(t) reads which follow". I can see
> that issue. Have you considered using the compiler barrier, barrier(), instead?
> From what I understand it will prevent the compiler from moving the memory accesses.
> This is what is currently done in __rdtgroup_move_task() and could be done here also?
A memory system (including those on x86) is allowed to reorder a store with a
later load, in addition to the compiler.
Also because the locations in question can be concurrently accessed by another
CPU, a compiler barrier would not be sufficient.
-Peter
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