linux-kernel - Re: [PATCH v2 5/5] psi: introduce psi monitor

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Message-ID: <20190117081314.GD10486@hirez.programming.kicks-ass.net>
Date:   Thu, 17 Jan 2019 09:13:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, lizefan@...wei.com, axboe@...nel.dk,
        dennis@...nel.org, Dennis Zhou <dennisszhou@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com
Subject: Re: [PATCH v2 5/5] psi: introduce psi monitor

On Wed, Jan 16, 2019 at 02:17:28PM -0500, Johannes Weiner wrote:

> > > Also, you probably want to use atomic_t for g->polling, because we
> > > (sadly) have architectures where regular stores and atomic ops don't
> > > work 'right'.
> > 
> > Oh, I see. Will do. Thanks!
> 
> Yikes, that's news to me too. Good to know.

See Documentation/atomic_t.txt, specifically the atomic_set() part in
SEMANTICS.

Archs that suffer this include (but are not limited to): parisc,
sparc32-smp, something arc.

And yes, I would dearly love to kill all SMP support for architectures
like that..