From: Suren Baghdasaryan <surenb@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tejun Heo <tj@kernel.org>,
lizefan@huawei.com, Johannes Weiner <hannes@cmpxchg.org>,
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
Subject: Re: [PATCH v3 5/5] psi: introduce psi monitor
Date: Tue, 29 Jan 2019 10:31:40 -0800 [thread overview]
Message-ID: <CAJuCfpHdtY7cRBfVP-+e9hQrTigStj2XK_qpk8z91HSKW+Y5WA@mail.gmail.com> (raw)
In-Reply-To: <CAJuCfpGxtGHsow002nd8Ao8mo9MaZQqZau_NLTMrZ8=aypTkig@mail.gmail.com>
On Tue, Jan 29, 2019 at 10:18 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Tue, Jan 29, 2019 at 4:38 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote:
> > > + atomic_set(&group->polling, polling);
> > > + /*
> > > + * Memory barrier is needed to order group->polling
> > > + * write before times[] read in collect_percpu_times()
> > > + */
> > > + smp_mb__after_atomic();
> >
> > That's broken, smp_mb__{before,after}_atomic() can only be used on
> > atomic RmW operations, something atomic_set() is _not_.
>
> Oh, I didn't realize that. After reading the following example from
> atomic_ops.txt I was under impression that smp_mb__after_atomic()
> would make changes done by atomic_set() visible:
>
> /* All memory operations before this call will
> * be globally visible before the clear_bit().
> */
> smp_mb__before_atomic();
> clear_bit( ... );
> /* The clear_bit() will be visible before all
> * subsequent memory operations.
> */
> smp_mb__after_atomic();
>
> but I'm probably missing something. Is there a more detailed
> description of these rules anywhere else?
I was referred to memory-barriers.txt that explains this clearly
stating that "These functions do not imply memory barriers.". Thanks
for noticing! Will change to smp_mb().
> Meanwhile I'll change smp_mb__after_atomic() into smp_mb(). Would that
> fix the ordering?
>
> > --
> > You received this message because you are subscribed to the Google Groups "kernel-team" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
> >
next prev parent reply other threads:[~2019-01-29 18:31 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-24 21:15 [PATCH v3 0/5] psi: pressure stall monitors v3 Suren Baghdasaryan
2019-01-24 21:15 ` [PATCH v3 1/5] fs: kernfs: add poll file operation Suren Baghdasaryan
2019-01-24 21:15 ` [PATCH v3 2/5] kernel: cgroup: " Suren Baghdasaryan
2019-01-24 21:15 ` [PATCH v3 3/5] psi: introduce state_mask to represent stalled psi states Suren Baghdasaryan
2019-01-28 21:22 ` Johannes Weiner
2019-01-24 21:15 ` [PATCH v3 4/5] psi: rename psi fields in preparation for psi trigger addition Suren Baghdasaryan
2019-01-28 21:23 ` Johannes Weiner
2019-01-24 21:15 ` [PATCH v3 5/5] psi: introduce psi monitor Suren Baghdasaryan
2019-01-28 21:26 ` Johannes Weiner
2019-01-28 23:53 ` Minchan Kim
2019-01-29 1:52 ` Suren Baghdasaryan
2019-01-29 18:35 ` Johannes Weiner
2019-01-29 10:44 ` Peter Zijlstra
2019-01-29 18:05 ` Suren Baghdasaryan
2019-01-29 12:38 ` Peter Zijlstra
2019-01-29 15:16 ` Peter Zijlstra
2019-01-29 18:25 ` Suren Baghdasaryan
2019-01-29 18:18 ` Suren Baghdasaryan
2019-01-29 18:31 ` Suren Baghdasaryan [this message]
2019-01-29 19:08 ` Peter Zijlstra
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