Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock()

[Matt Turner]

On Tue, Jan 14, 2014 at 3:03 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 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.

That's right, and thanks for the heads-up. Alpha can only address 4
and 8 bytes atomically. (LDL_L, LDQ_L, STL_C, STQ_C).

The Byte-Word extension in EV56 doesn't add new atomics, so in fact no
Alphas can address < 4 bytes atomically.
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