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

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Message-ID: <4957DCC3.3060505@redhat.com>
Date:	Sun, 28 Dec 2008 22:08:35 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>
CC:	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

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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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