linux-kernel - Re: [PATCH v2 2/2] virtio-ring: Allocate indirect buffers from cache when possible

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Date:	Mon, 10 Sep 2012 17:52:41 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, avi@...hat.com,
	Sasha Levin <levinsasha928@...il.com>, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 2/2] virtio-ring: Allocate indirect buffers from cache
 when possible

Il 06/09/2012 07:02, Michael S. Tsirkin ha scritto:
>> > It might be worth just unconditionally having a cache for the 2
>> > descriptor case.  This is what I get with qemu tap, though for some
>> > reason the device features don't have guest or host CSUM, so my setup is
>> > probably screwed:
> Yes without checksum net core always linearizes packets, so yes it is
> screwed.
> For -net, skb always allocates space for 17 frags + linear part so
> it seems sane to do same in virtio core, and allocate, for -net,
> up to max_frags + 1 from cache.
> We can adjust it: no _SG -> 2 otherwise 18.
> 
> Not sure about other drivers, maybe really use 2 there for now.

2 should also be good for virtio-blk and virtio-scsi 4KB random rw
workloads.

Paolo

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