netdev - Re: [PATCH] net: Update netdev_alloc_frag to work more efficiently with TCP and GRO

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Message-ID: <1340180223.4604.828.camel@edumazet-glaptop>
Date:	Wed, 20 Jun 2012 10:17:03 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	jeffrey.t.kirsher@...el.com
Subject: Re: [PATCH] net: Update netdev_alloc_frag to work more efficiently
 with TCP and GRO

On Wed, 2012-06-20 at 07:36 +0200, Eric Dumazet wrote:

> I tested this idea one month ago and got not convincing results, because
> the branch was taken half of the time.
> 
> The cases where page can be reused is probably specific to ixgbe because
> it uses a different allocator for the frags themselves.
> netdev_alloc_frag() is only used to allocate the skb head.
> 
> For typical nics, we allocate frags to populate the RX ring _way_ before
> packet is received by the NIC.
> 
> Then, I played with using order-2 pages instead of order-0 ones if
> PAGE_SIZE < 8192.
> 
> No clear win either, but you might try this too.

By the way, big cost in netdev_alloc_frag() is the irq masking/restore
We probably could have a version for softirq users...

Another idea would also use a pool of pages, instead of a single one,
if we want to play with the "clear the offset if page count is one"
idea.

Strange, I did again benchs with order-2 allocations and got good
results this time, but with latest net-next, maybe things have changed
since last time I did this.

(netdev_alloc_frag(), get_page_from_freelist() and put_page() less
prevalent in perf results)


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