linux-kernel - Re: [PATCH 0/3] Remove interrupt stack table usage from x86

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Message-ID: <20081228203425.GF496@one.firstfloor.org>
Date:	Sun, 28 Dec 2008 21:34:25 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	x86@...nel.org, linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/3] Remove interrupt stack table usage from x86_64 kernel

On Sun, Dec 28, 2008 at 10:08:35PM +0200, Avi Kivity wrote:
> Avi Kivity wrote:
> >Avi Kivity wrote:
> >>1. Add per-cpu IDT
> >
> >Or we could have just two IDTs - one with IST and one without.  I 
> >clocked LIDT at 58 cycles (and we need two per heavyweight switch), so 
> >it's not that wonderful.
> 
> This makes the whole thing unworthwhile.  The vmload/vmsave pair costs 
> only 200 cycles (I should have started with this), and 120 cycles on the 
> heavyweight path plus complexity are not worth 200 cycles on the 
> lightweight path.

Actually to switch ISTs you need to change the TSS, not the IDT.
But I suppose that won't be any faster.

-Andi
-- 
ak@...ux.intel.com
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