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Date: Wed, 05 May 2010 10:30:18 +0300 From: Avi Kivity <avi@...hat.com> To: "H. Peter Anvin" <hpa@...or.com> CC: Suresh Siddha <suresh.b.siddha@...el.com>, Brian Gerst <brgerst@...il.com>, "Cui, Dexuan" <dexuan.cui@...el.com>, Sheng Yang <sheng@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org> Subject: Re: [PATCH 1/2] x86: eliminate TS_XSAVE On 05/04/2010 09:24 PM, H. Peter Anvin wrote: > > I would like to request one change, however. I would like to see the > alternatives code to be: > > movb $0,reg > movb $1,reg > > ... instead of using xor (which has to be padded with NOPs, which is of > course pointless since the slot is a fixed size.) Right. > I would suggest using > a byte-sized variable instead of a dword-size variable to save a few > bytes, too. > I used a bool, and the code already compiles to a byte mov. Though it could be argued that a word instruction is better since it avoids a false dependency, and allows a preceding instruction that modifies %reg to be executed after the mov instruction. > Once the jump label framework is integrated and has matured, I think we > should consider using it to save the mov/test/jump. > IIRC that has an implied unlikely() which isn't suitable here? Perhaps the immediate values patches. -- error compiling committee.c: too many arguments to function -- 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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