Date:   Wed, 8 Mar 2023 16:01:12 +0100
From:   Frederic Weisbecker <frederic@kernel.org>
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, Qiuxu Zhuo <qiuxu.zhuo@intel.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-doc@vger.kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
        rcu@vger.kernel.org, urezki@gmail.com
Subject: Re: [PATCH v3] rcu: Add a minimum time for marking boot as completed
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On Wed, Mar 08, 2023 at 05:52:50AM -0800, Joel Fernandes wrote:
> Just to add to previous reply:
> 
> One thing to consider is that it is more of a performance improvement for
> booting in expedited mode to fallback to normal later, than a bug
> fix. Repeated synchronize_rcu() can easily add 100s of milliseconds and to
> remedy that — a conversion of the call from normal API to the expedited API
> will not help.

2 things to consider:

1) Is it this about specific calls to synchronize_rcu() that repeat a lot
   and thus create such measurable impact? If so the specific callsites should
   be considered for a conversion.

2) Is it about lots of different calls to synchronize_rcu() that gather a big
   noise? Then the solution is different.

Again without proper analysis, what do we know?

Thanks.