linux-kernel - Re: [PATCH 2/2] sched/topology: Expose numa

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Message-Id: <20180831115350.GC8437@linux.vnet.ibm.com>
Date:   Fri, 31 Aug 2018 04:53:50 -0700
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Benjamin Herrenschmidt <benh@....ibm.com>
Subject: Re: [PATCH 2/2] sched/topology: Expose numa_mask set/clear functions
 to arch

* Peter Zijlstra <peterz@...radead.org> [2018-08-31 13:26:39]:

> On Fri, Aug 31, 2018 at 01:12:53PM +0200, Peter Zijlstra wrote:
> > NAK, not until you've fixed every cpu_to_node() user in the kernel to
> > deal with that mask changing.
> 
> Also, what happens if userspace reads that information; uses libnuma and
> then you go and shift the world underneath their feet?
> 
> > This is absolutely insane.
> 

The topology events are suppose to be very rare.
>From whatever small experiments I have done till now, unless tasks are
bound to both cpu and memory, they seem to be coping well with topology
updates. I know things weren't optimal after a topology change but they
worked. Now after 051f3ca02e46 "Introduce NUMA identity node sched
domain", systems stall. I am only exploring at ways to keep them working
as much as they were before that commit.

-- 
Thanks and Regards
Srikar Dronamraju