linux-kernel - Re: [PATCH, resend] x86-64: improve insn scheduling in SAVE_ARGS

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Date:	Mon, 27 Feb 2012 08:11:40 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>, <ak@...ux.intel.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH, resend] x86-64: improve insn scheduling in
 SAVE_ARGS_IRQ

>>> On 24.02.12 at 21:21, "H. Peter Anvin" <hpa@...or.com> wrote:
> On 02/24/2012 03:55 AM, Jan Beulich wrote:
>>  	leaq -RBP(%rsp),%rdi	/* arg1 for handler */
>> -	testl $3, CS(%rdi)
>> +	testl $3, CS-RBP(%rsi)
>>  	je 1f
> 
> IIRC there is no imm8 version of testl; could this be a testb instead or
> is that going to cause stalls on some platforms you think?

As far as I'm aware, memory operations don't suffer "partial register
stalls" or alike, so yes, using a testb here ought to be appropriate.

Jan

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