linux-kernel - Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write

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Message-ID: <20140114110307.GW7572@laptop.programming.kicks-ass.net>
Date:	Tue, 14 Jan 2014 12:03:07 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel J Blueman <daniel@...ascale.com>
Cc:	Waiman Long <waiman.long@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, rth@...ddle.net,
	ink@...assic.park.msu.ru, mattst88@...il.com,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock()

On Tue, Jan 14, 2014 at 10:28:23AM +0800, Daniel J Blueman wrote:
> >Peter,
> >
> >I found out that the build failure was caused by the fact that the
> >__native_word() macro (used internally by compiletime_assert_atomic())
> >allows only a size of 4 or 8 for x86-64. The data type that I used is a
> >byte. Is there a reason why byte and short are not considered native?
> 
> It seems likely it was implemented like that since there was no existing
> need; long can be relied on as the largest native type, so this should
> suffice and works here:

There's Alphas that cannot actually atomically adres a byte; I do not
konw if Linux cares about them, but if it does, we cannot in fact rely
on this in generic primitives like this.
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