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Date: Tue, 5 Jan 2010 08:14:51 -0800 (PST) From: Linus Torvalds <torvalds@...ux-foundation.org> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> cc: Minchan Kim <minchan.kim@...il.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, cl@...ux-foundation.org, "hugh.dickins" <hugh.dickins@...cali.co.uk>, Nick Piggin <nickpiggin@...oo.com.au>, Ingo Molnar <mingo@...e.hu> Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() On Tue, 5 Jan 2010, Linus Torvalds wrote: > > Lookie here: > > - arch/x86/Kconfig.cpu: > > config X86_XADD > def_bool y > depends on X86_32 && !M386 > > - arch/x86/Kconfig: > > config RWSEM_GENERIC_SPINLOCK > def_bool !X86_XADD > > config RWSEM_XCHGADD_ALGORITHM > def_bool X86_XADD > > it looks like X86_XADD only gets enabled on 32-bit builds. Which means > that x86-64 in turn seems to end up always using the slower "generic > spinlock" version. Sadly, it's not as easy as just changing the X86_XADD "depends on" to say "X86_64 || !M386" instead. That just results in kernel/built-in.o: In function `up_read': (.text+0x2d8e5): undefined reference to `call_rwsem_wake' etc, because the x86-64 code has obviously never seen the optimized call-paths, and they need the asm wrappers for full semantics. Oh well. Somebody who is bored might look at trying to make the wrapper code in arch/x86/lib/semaphore_32.S work on x86-64 too. It should make the successful rwsem cases much faster. Linus -- 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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