linux-kernel - Re: [PATCH v2 2/3] vmstat: skip periodic vmstat update for nohz full CPUs

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Date:   Mon, 5 Jun 2023 16:14:18 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v2 2/3] vmstat: skip periodic vmstat update for nohz full
 CPUs

On Mon, Jun 05, 2023 at 08:57:15PM +0200, Michal Hocko wrote:
> > Guest initiated I/O, since the host CPU is isolated.
> 
> Make it explicit in the changelog.

I think better use of our time would be to focus on

https://lkml.iu.edu/hypermail/linux/kernel/2209.1/01263.html

1) Operate in terms of add CPU, remove CPU on sysfs (to avoid races).
2) Don't allow all CPUs to be marked as "block_interf".
3) Remove percpu rwsem lock.

> I am just wondering how you can achieve your strict deadlines when IO is
> involved but that is another story I guess.

IO can be submitted when the ELF binary and libraries are read
from the virtual disk, for example.