linux-kernel - Re: [PATCH 1/3] kvm: memslots: track id_to_index changes during the insertion sort

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Date:	Fri, 14 Nov 2014 15:41:36 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, yoshikawa_takuya_b1@....ntt.co.jp
Subject: Re: [PATCH 1/3] kvm: memslots: track id_to_index changes during the
 insertion sort

2014-11-14 15:17+0100, Igor Mammedov:
> > (We'll have to change it into an interval tree, or something, if the
> >  number of slots rises anyway.)
> Only if it rises to huge amount, I've played with proposed 512 memslots
> and it takes ~10000 cycles which is 5% of current heapsort overhead.
> Taking in account that it's slow path anyway, it's unlikely that there
> would be need to speedup this case even more.

Yes, your improvement is great and would work even for higher amounts.

I meant that our lookup is currently pretty sad -- O(N) that is
presumably optimized by looking at the largest regions first.

Maybe we would benefit from O(log N) lookup even with 128 memslots.
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