linux-kernel - Re: atomic_inc and spin_lock

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Message-ID: <20141219000416.689f3ab7@mdontu-l.dsd.ro>
Date:	Fri, 19 Dec 2014 00:04:16 +0200
From:	Mihai Donțu <mihai.dontu@...il.com>
To:	"Rogelio M. Serrano Jr." <rogelios664@...il.com>
Cc:	linux-kernel@...r.kernel.org, pageexec@...email.hu
Subject: Re: atomic_inc and spin_lock_irq

On Thu, 18 Dec 2014 21:07:46 +0000 Rogelio M. Serrano Jr. wrote:
> whats the difference between:
> 
> atomic_inc(&port->count);

It is intended to atomically increment a variable of a standard size
(int/long). See [1] for more information.

> and
> 
> spin_lock_irq(&port->lock);
> ++port->count;
> spin_unlock_irq(&port->lock);

These are intended to be used when larger changes are to be made in an
atomic fashion (not just increments). See [2] for details and [3] for
an example.

[1] https://en.wikipedia.org/wiki/Fetch-and-add
[2] http://lxr.free-electrons.com/source/include/linux/spinlock_api_smp.h#L104
[3] http://lxr.free-electrons.com/source/arch/x86/mm/mmio-mod.c#L265

-- 
Mihai Donțu
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