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Date: Tue, 14 Jan 2014 15:44:43 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Richard Henderson <rth@...ddle.net> Cc: Matt Turner <mattst88@...il.com>, Peter Zijlstra <peterz@...radead.org>, Daniel J Blueman <daniel@...ascale.com>, Waiman Long <waiman.long@...com>, Linux Kernel <linux-kernel@...r.kernel.org>, Ivan Kokshaysky <ink@...assic.park.msu.ru>, 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 10:01:04AM -0800, 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@...radead.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. Which means that Alpha should be able to similarly emulate 1-byte and 2-byte atomics, correct? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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