linux-kernel - Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

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Message-ID: <20081105181558.GF7286@localhost>
Date:	Wed, 5 Nov 2008 21:15:58 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Alexander van Heukelum <heukelum@...lshack.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	heukelum@...tmail.fm, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, lguest@...abs.org,
	jeremy@...source.com, Steven Rostedt <srostedt@...hat.com>,
	Mike Travis <travis@....com>
Subject: Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

[Andi Kleen - Tue, Nov 04, 2008 at 06:05:01PM +0100]
| > not taking into account the cost of cs reading (which I
| > don't suspect to be that expensive apart from writting,
| 
| GDT accesses have an implied LOCK prefix. Especially
| on some older CPUs that could be slow.
| 
| I don't know if it's a problem or not but it would need
| some careful benchmarking on different systems to make sure interrupt 
| latencies are not impacted.
| 
| Another reason I would be also careful with this patch is that
| it will likely trigger slow paths in JITs like qemu/vmware/etc.
| 
| Also code segment switching is likely not something that
| current and future micro architectures will spend a lot of time optimizing.
| 
| I'm not sure that risk is worth the small improvement in code
| size.
| 
| An alternative BTW to having all the stubs in the executable
| would be to just dynamically generate them when the interrupt
| is set up. Then you would only have the stubs around for the 
| interrupts which are actually used.
| 
| -Andi
| 

Thanks a lot for comments, Andi!

		- Cyrill -
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