netdev - Re: [PATCH] vhost: support upto 509 memory regions

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Date:	Tue, 17 Feb 2015 18:09:06 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Igor Mammedov <imammedo@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] vhost: support upto 509 memory regions



On 17/02/2015 16:02, Igor Mammedov wrote:
>> > 
>> > Not if there are about 6 regions, I think.
> When memslots where increased to 509 and look up of them was replaced on
> binary search results were on par with linear search for a default 13 memslots VM.
> 
> Adding LRU

You mean MRU. :)

> cache helped to shave ~40% of cycles for sequential lookup workloads.

It's a bit different for vhost because you can have up to four "things"
being looked up at the same time:

- the s/g list that will end up in the skb

- the avail/used ring

- the virtio buffers

- the virtio indirect buffers

So you probably need multiple MRU caches.  But yes, MRU can help a lot.

Paolo
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