netdev - Re: [PATCH net-next v2 3/4] virtio-net: auto-tune mergeable rx buffer size for improved performance

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Message-ID: <20140109064807.GC19559@redhat.com>
Date:	Thu, 9 Jan 2014 08:48:07 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Michael Dalton <mwdalton@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>,
	lf-virt <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next v2 3/4] virtio-net: auto-tune mergeable rx
 buffer size for improved performance

On Wed, Jan 08, 2014 at 07:41:58PM -0800, Michael Dalton wrote:
> Sorry, forgot to mention - if we want to explore combining the buffer
> address and truesize into a single void *, we could also exploit the
> fact that our size ranges from aligned GOOD_PACKET_LEN to PAGE_SIZE, and
> potentially encode fewer values for truesize (and require a smaller
> alignment than 256). The prior e-mails discussion of 256 byte alignment
> with 256 values is just one potential design point.
> 
> Best,
> 
> Mike

Good point. I think we should keep the option to
make buffers bigger than 4K, so I think we should start with 256
alignment, then see if there are workloads that are improved by smaller
alignment.

Can you add wrapper inline functions to pack/unpack size and
buffer pointer to/from void *?
This way it will be easy to experiment with different alignments.

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