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Date:   Wed, 24 Mar 2021 11:54:32 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org,
        "linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
        debian-ia64 <debian-ia64@lists.debian.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Sergei Trofimovich <slyfox@gentoo.org>,
        Anatoly Pugachev <matorola@gmail.com>
Subject: Re: [PATCH] ia64: Ensure proper NUMA distance and possible map
 initialization
Message-Id: <20210324115432.4102cd93d35a2edb1742dec7@linux-foundation.org>
In-Reply-To: <20210318130617.896309-1-valentin.schneider@arm.com>
References: <20210318130617.896309-1-valentin.schneider@arm.com>
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On Thu, 18 Mar 2021 13:06:17 +0000 Valentin Schneider <valentin.schneider@arm.com> wrote:

> John Paul reported a warning about bogus NUMA distance values spurred by
> commit:
> 
>   620a6dc40754 ("sched/topology: Make sched_init_numa() use a set for the deduplicating sort")
> 
> In this case, the afflicted machine comes up with a reported 256 possible
> nodes, all of which are 0 distance away from one another. This was
> previously silently ignored, but is now caught by the aforementioned
> commit.
> 
> The culprit is ia64's node_possible_map which remains unchanged from its
> initialization value of NODE_MASK_ALL. In John's case, the machine doesn't
> have any SRAT nor SLIT table, but AIUI the possible map remains untouched
> regardless of what ACPI tables end up being parsed. Thus, !online &&
> possible nodes remain with a bogus distance of 0 (distances \in [0, 9] are
> "reserved and have no meaning" as per the ACPI spec).
> 
> Follow x86 / drivers/base/arch_numa's example and set the possible map to
> the parsed map, which in this case seems to be the online map.
> 
> Link: http://lore.kernel.org/r/255d6b5d-194e-eb0e-ecdd-97477a534441@physik.fu-berlin.de
> Fixes: 620a6dc40754 ("sched/topology: Make sched_init_numa() use a set for the deduplicating sort")
> Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> ---
> This might need an earlier Fixes: tag, but all of this is quite old and
> dusty (the git blame rabbit hole leads me to ~2008/2007)
> 

Thanks.  Is this worth a cc:stable tag?