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Date: Thu, 17 Jan 2019 09:13:14 +0100
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 5/5] psi: introduce psi monitor
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To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Suren Baghdasaryan <surenb@google.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Tejun Heo <tj@kernel.org>, lizefan@huawei.com, axboe@kernel.dk, dennis@kernel.org, Dennis Zhou <dennisszhou@gmail.com>, Ingo Molnar <mingo@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Jonathan Corbet <corbet@lwn.net>, cgroups@vger.kernel.org, linux-mm <linux-mm@kvack.org>, linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, kernel-team@android.com

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..