From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Rik van Riel <riel@surriel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Andre Wild <wild@linux.vnet.ibm.com>
Subject: Re: [PATCH] sched/topology: Use Identity node only if required
Date: Wed, 8 Aug 2018 09:58:41 +0200 [thread overview]
Message-ID: <20180808075840.GO2494@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1533712172-11428-1-git-send-email-srikar@linux.vnet.ibm.com>
On Wed, Aug 08, 2018 at 12:39:31PM +0530, Srikar Dronamraju wrote:
> With Commit 051f3ca02e46 ("sched/topology: Introduce NUMA identity node
> sched domain") scheduler introduces an extra numa level. However that
> leads to
>
> - numa topology on 2 node systems no more marked as NUMA_DIRECT. After
> this commit, it gets reported as NUMA_BACKPLANE. This is because
> sched_domains_numa_level now equals 2 on 2 node systems.
>
> - Extra numa sched domain that gets added and degenerated on most
> machines. The Identity node is only needed on very few systems.
> Also all non-numa systems will end up populating
> sched_domains_numa_distance and sched_domains_numa_masks tables.
>
> - On shared lpars like powerpc, this extra sched domain creation can
> lead to repeated rcu stalls, sometimes even causing unresponsive
> systems on boot. On such stalls, it was noticed that
> init_sched_groups_capacity() (sg != sd->groups is always true).
The idea was that if the topology level is redundant (as it often is);
then the degenerate code would take it out.
Why is that not working (right) and can we fix that instead?
next prev parent reply other threads:[~2018-08-08 7:59 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-08 7:09 [PATCH] sched/topology: Use Identity node only if required Srikar Dronamraju
2018-08-08 7:58 ` Peter Zijlstra [this message]
2018-08-08 8:19 ` Srikar Dronamraju
2018-08-08 8:43 ` Peter Zijlstra
2018-08-08 9:30 ` Peter Zijlstra
2018-08-10 16:45 ` Srikar Dronamraju
2018-08-29 8:43 ` Peter Zijlstra
2018-08-29 8:57 ` Peter Zijlstra
2018-08-31 10:22 ` Srikar Dronamraju
2018-08-31 10:41 ` Peter Zijlstra
2018-08-31 11:26 ` Srikar Dronamraju
2018-08-31 12:06 ` Peter Zijlstra
[not found] <reply-to=<20180808081942.GA37418@linux.vnet.ibm.com>
2018-08-10 17:00 ` [PATCH 1/2] sched/topology: Set correct numa topology type Srikar Dronamraju
2018-08-10 17:00 ` [PATCH 2/2] sched/topology: Expose numa_mask set/clear functions to arch Srikar Dronamraju
2018-08-29 8:02 ` Peter Zijlstra
2018-08-31 10:27 ` Srikar Dronamraju
2018-08-31 11:12 ` Peter Zijlstra
2018-08-31 11:26 ` Peter Zijlstra
2018-08-31 11:53 ` Srikar Dronamraju
2018-08-31 12:05 ` Peter Zijlstra
2018-08-31 12:08 ` Peter Zijlstra
2018-08-21 11:02 ` [PATCH 1/2] sched/topology: Set correct numa topology type Srikar Dronamraju
2018-08-21 13:59 ` Peter Zijlstra
2018-09-10 10:06 ` [tip:sched/core] sched/topology: Set correct NUMA " tip-bot for Srikar Dronamraju
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