linux-kernel - Re: [RFC PATCH-tip v4 10/10] locking/rwsem: Add a boot parameter to reader spinning threshold

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Message-ID: <20160824040007.GA17186@linux-80c1.suse>
Date:   Tue, 23 Aug 2016 21:00:07 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Waiman Long <Waiman.Long@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-alpha@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        Jason Low <jason.low2@...com>,
        Dave Chinner <david@...morbit.com>,
        Jonathan Corbet <corbet@....net>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>
Subject: Re: [RFC PATCH-tip v4 10/10] locking/rwsem: Add a boot parameter to
 reader spinning threshold

On Thu, 18 Aug 2016, Waiman Long wrote:

>The default reader spining threshold is current set to 4096. However,
>the right reader spinning threshold may vary from one system to
>another and among the different architectures. This patch adds a new
>kernel boot parameter to modify the threshold value. This enables
>better tailoring to the needs of different systems as well as for
>testing purposes.

It also means that those systems could very easily be incorrectly tailored.
(and worse case scenario: reboot, is obviously a terrible way to get rid
of any issues). I very much disagree with exposing this sort of core stuff,
it should work well for everyone out of the box, not relying on users to
properly configure this.

Thanks,
Davidlohr