linux-kernel - Re: [PATCH v1 1/4] spidev: Do not use atomic bit operations when allocating minor

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Message-ID: <YjyAFNYpDjSQnIN1@sirena.org.uk>
Date:   Thu, 24 Mar 2022 14:28:36 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/4] spidev: Do not use atomic bit operations when
 allocating minor

On Thu, Mar 24, 2022 at 11:24:26AM +0200, Andy Shevchenko wrote:
> On Wed, Mar 23, 2022 at 07:06:25PM +0000, Mark Brown wrote:

> > Yes, it's not needed but what meaningful harm does it do?

> There are basically two points:

> 1) in one driver the additional lock may not be influential, but
>    if many drivers will do the same, it will block CPUs for no
>    purpose;

> 2) derived from the above, if one copies'n'pastes the code, esp.
>    using spin locks, it may become an unneeded code and performance
>    degradation.

I think if these are serious issues they need to be addressed in the API
so that code doing the fancy unlocked stuff that needs atomicity is the
code that has the __ and looks like it's doing something tricky and
peering into internals.

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