linux-kernel - Re: [PATCH v2] cpuset: restore sanity to cpuset_cpus_allowed

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Message-ID: <CAL1p7m7T+ASfEd9dXEDg59XQEdp=eUE9fj5q-7hyEXat=_hL0A@mail.gmail.com>
Date:   Thu, 13 Jun 2019 10:52:22 -0400
From:   Joel Savitz <jsavitz@...hat.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Li Zefan <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>,
        Waiman Long <longman@...hat.com>, Phil Auld <pauld@...hat.com>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cpuset: restore sanity to cpuset_cpus_allowed_fallback()

I just did a quick test on a patched kernel to check on that "no
longer affine to..." message:

# nproc
64

# taskset -p 4 $$
pid 2261's current affinity mask: ffffffffffffffff
pid 2261's new affinity mask: 4
# echo off > /sys/devices/system/cpu/cpu2/online
# taskset -p $$
pid 2261's current affinity mask: fffffffffffffffb
# echo on > /sys/devices/system/cpu/cpu2/online
# taskset -p $$
pid 2261's current affinity mask: ffffffffffffffff

# dmesg | tail -5
[  143.996375] process 2261 (bash) no longer affine to cpu2
[  143.996657] IRQ 114: no longer affine to CPU2
[  144.007472] IRQ 227: no longer affine to CPU2
[  144.013460] smpboot: CPU 2 is now offline
[  162.685519] smpboot: Booting Node 0 Processor 2 APIC 0x4

dmesg output is observably the same on patched and unpatched kernels
in this case.

The only difference in output is that on an unpatched kernel, the last
`taskset -p $$` outputs:
pid 2274's current affinity mask: fffffffffffffffb
Which is the behavior that this patch aims to modify

This case, which I believe is generalizable, demonstrates that we
retain the "no longer affine to..." output on a kernel with this
patch.

Best,
Joel Savitz



On Thu, Jun 13, 2019 at 8:02 AM Michal Koutný <mkoutny@...e.com> wrote:
>
> On Tue, May 28, 2019 at 02:10:37PM +0200, Michal Koutný  <MKoutny@...e.com> wrote:
> > Although, on v1 we will lose the "no longer affine to..." message
> > (which is what happens in your demo IIUC).
> FWIW, I was wrong, off by one 'state' transition. So the patch doesn't
> cause change in messaging (not tested though).