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Date: Mon, 17 Nov 2008 22:22:16 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Alexander van Heukelum <heukelum@fastmail.fm>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>,
       Alexander van Heukelum <heukelum@lusi.uni-sb.de>,
       Glauber Costa <gcosta@redhat.com>
Subject: Re: [RFC] x86: save_args out of line
Message-ID: <20081117192216.GA9944@localhost>
References: <1226845741-12470-1-git-send-email-heukelum@fastmail.fm> <1226845741-12470-2-git-send-email-heukelum@fastmail.fm> <20081117125317.GK6703@one.firstfloor.org> <1226936257.32609.1285214311@webmail.messagingengine.com> <20081117182340.GN6703@one.firstfloor.org>
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[Andi Kleen - Mon, Nov 17, 2008 at 07:23:40PM +0100]
...
| 
| Ok. Hopefully it's worth the effort. The branch misprediction bubble
| should not be too bad, perhaps it'll make up for the other cycles
| you're adding. But even if it doesn't decreasing cache line foot print is 
| always a good thing.
...

May I turn in? :)

Original .macro interrupt func has

	testl $3, CS(%rdi)
	je 1f
	SWAPGS
1:	incl %gs:pda_irqcount
	jne 2f
	pop %rax
	mov %gs:pda_irqstackptr,%rsp
	push %rax
2:	TRACE_IRQS_OFF

Wouldn't we help the branch predictor a bit by

	testl $3, CS(%rdi)
	je 1f
	SWAPGS
	jne 2f
1:	pop %rax
	mov %gs:pda_irqstackptr,%rsp
	push %rax	
2:	incl %gs:pda_irqcount
	TRACE_IRQS_OFF

I hope I didn't miss anything but maybe it's just a churning
or plain wrong. Don't shoot me :)

		- Cyrill -
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