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

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Date:	Mon, 30 Dec 2013 13:38:19 +0800
From:	Jason Wang <jasowang@...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>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	lf-virt <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next 3/3] net: auto-tune mergeable rx buffer size
 for improved performance

On 12/28/2013 05:41 AM, Michael Dalton wrote:
> I'm working on a followup patchset to address current feedback. I think
> it will be cleaner to do a debugfs implementation for per-receive queue
> packet buffer size exporting, so I'm trying that out.
>
> On Thu, Dec 26, 2013 at 7:04 PM, Jason Wang <jasowang@...hat.com> wrote:
>> We can make this more accurate by using extra data structure to track
>> the real buf size and using it as token.
> I agree -- we can do precise buffer total len tracking. Something like
> struct mergeable_packet_buffer_ctx {
>    void *buf;
>    unsigned int total_len;
> };
>
> Each receive queue could have a pointer to an array of N buffer contexts,
> where N is queue size (kzalloc'd in init_vqs or similar). That would
> allow us to allocate all of our buffer context data at startup.
>
> Would this be preferred to the current approach or is there another
> approach you would prefer? All other things being equal, having precise
> length tracking is advantageous, so I'm inclined to try this out and
> see how it goes.
>
> I think this is a big design point - for example, if we have an extra
> buffer context structure, then per-receive queue frag allocators are not
> required for auto-tuning and we can reduce the number of patches in
> this patchset.

Not required but better keep it. Consider we may have multiple
virtio-net cards, using per-receive queue frag may increase the
possibility of coalescing.
>
> I'm happy to implement either way.  Thanks!
>
> Best,
>
> Mike

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