Re: [PATCH 0/3] Remove interrupt stack table usage from x86_64 kernel

From: Avi Kivity
Date: Sun Dec 28 2008 - 15:28:56 EST


Andi Kleen wrote:
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.

I can't touch the TSS (that's the starting point of the exercise). The plan was to have a copy of the IDT with all IST pointers zeroed out (or to have per-cpu IDT and zero out the IST pointers when entering guest mode, restoring them on context switch).

It's not worth it though.

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

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