Messages in this thread | | | Date | Tue, 14 Jan 2014 14:09:30 -0500 | From | Waiman Long <> | Subject | Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock() |
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On 01/14/2014 01:01 PM, Richard Henderson wrote: > On 01/14/2014 09:08 AM, Matt Turner wrote: >> On Tue, Jan 14, 2014 at 3:03 AM, Peter Zijlstra<peterz@infradead.org> 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. >> > Emulated with aligned 4 byte atomics, and masking. The same is true for arm, > ppc, mips which, depending on cpu, also lack< 4 byte atomics. >
I would like to know if the action of writing out a byte (e.g. *byte = 0) is atomic in those architectures or is emulated by a compiler-generated software read-modify-write.
-Longman
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