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Message-ID: <6690c4c7119839a784d0d96523e832a10e04fcca.camel@redhat.com>
Subject: Re: [PATCH 00/21] rcu/context-tracking: Merge RCU eqs-dynticks
 counter to context tracking v2
From:   Nicolas Saenz Julienne <nsaenzju@redhat.com>
To:     Frederic Weisbecker <frederic@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Phil Auld <pauld@redhat.com>,
        Alex Belits <abelits@marvell.com>,
        Xiongfeng Wang <wangxiongfeng2@huawei.com>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Yu Liao <liaoyu15@huawei.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Uladzislau Rezki <uladzislau.rezki@sony.com>,
        Joel Fernandes <joel@joelfernandes.org>
Date:   Wed, 18 May 2022 17:33:02 +0200
In-Reply-To: <20220503100051.2799723-1-frederic@kernel.org>
References: <20220503100051.2799723-1-frederic@kernel.org>
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On Tue, 2022-05-03 at 12:00 +0200, Frederic Weisbecker wrote:
> This mixes up the RCU dynticks counter and the context tracking state
> updates into a single atomic instruction. This may serve several
> purposes:
>=20
> 1) Improve CPU isolation with deferring some disturbances until sensitive
>    userspace workload completes and goes to the kernel. This can take
>    several forms, for example smp_call_function_housekeeping() or
>    on_each_housekeeping_cpu() to enqueue and execute work on all
>    housekeeping CPUs. Then an atomic operation on ct->state can defer
>    the work on nohz_full CPUs until they run in kernel (or IPI them
>    if they are in kernel mode), see this proposal by Peter:
>    https://lore.kernel.org/all/20210929151723.162004989@infradead.org/#r
>=20
> 2) Unearth sysidle (https://git.kernel.org/pub/scm/linux/kernel/git/paulm=
ck/linux-rcu.git/commit/?h=3Dsysidle.2017.05.11a&id=3Dfe5ac724d81a3c7803e60=
c2232718f212f3f38d4)
>    This feature allowed to shutdown the tick on the last housekeeping
>    CPU once the rest of the system is fully idle. We needed some proper
>    fully ordered context tracking for that.
>=20
> Inspired by Peterz: https://lore.kernel.org/all/20210929151723.162004989@=
infradead.org
>=20
> Passed 100 hours of TREE01.
>=20
> ---

For the whole series:

Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>

Thanks!

--=20
Nicol=C3=A1s S=C3=A1enz