linux-kernel - Re: [RFC] x86: save

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Message-ID: <20081117192216.GA9944@localhost>
Date:	Mon, 17 Nov 2008 22:22:16 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Alexander van Heukelum <heukelum@...tmail.fm>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander van Heukelum <heukelum@...i.uni-sb.de>,
	Glauber Costa <gcosta@...hat.com>
Subject: Re: [RFC] x86: save_args out of line

[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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