linux-kernel - Re: [PATCH 08/10] x86-32: support atomic64

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Date:	Thu, 18 Feb 2010 11:58:01 +0100
From:	Luca Barbieri <luca@...a-barbieri.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...e.hu, hpa@...or.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] x86-32: support atomic64_t on 386/486 UP/SMP

> IIRC we dropped <i586 SMP support, and since we don't have a PMU on
> those chips atomic64_t doesn't need to be NMI safe, so a simple
> UP-IRQ-disable implementation should suffice.

We need the generic version with spinlocks for other architectures,
and reusing it is the cheapest way to support 386/486.

We thus get 386/486 SMP for free, and on UP the spinlocks simplify to
just IRQ disabling.

The only thing we could do is to #ifdef out the hashed spinlock array
in the generic implementation on UP builds, which would save about 1KB
of memory.
That is independent from this patch though.
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