netdev - Re: [PATCH] mlx4_en: map entire pages to increase throughput

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Message-Id: <20120719.105354.1512390551884485493.davem@davemloft.net>
Date:	Thu, 19 Jul 2012 10:53:54 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	cascardo@...ux.vnet.ibm.com
Cc:	netdev@...r.kernel.org, yevgenyp@...lanox.co.il,
	ogerlitz@...lanox.com, amirv@...lanox.com,
	brking@...ux.vnet.ibm.com, leitao@...ux.vnet.ibm.com,
	klebers@...ux.vnet.ibm.com
Subject: Re: [PATCH] mlx4_en: map entire pages to increase throughput

From: Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
Date: Mon, 16 Jul 2012 14:01:53 -0300

> In its receive path, mlx4_en driver maps each page chunk that it pushes
> to the hardware and unmaps it when pushing it up the stack. This limits
> throughput to about 3Gbps on a Power7 8-core machine.
> 
> One solution is to map the entire allocated page at once. However, this
> requires that we keep track of every page fragment we give to a
> descriptor. We also need to work with the discipline that all fragments will
> be released (in the sense that it will not be reused by the driver
> anymore) in the order they are allocated to the driver.
> 
> This requires that we don't reuse any fragments, every single one of
> them must be reallocated. We do that by releasing all the fragments that
> are processed and only after finished processing the descriptors, we
> start the refill.
> 
> We also must somehow guarantee that we either refill all fragments in a
> descriptor or none at all, without resorting to giving up a page
> fragment that we would have already given. Otherwise, we would break the
> discipline of only releasing the fragments in the order they were
> allocated.
> 
> This has passed page allocation fault injections (restricted to the
> driver by using required-start and required-end) and device hotplug
> while 16 TCP streams were able to deliver more than 9Gbps.
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>

I have not seen any reasonable objections to this patch, so I have
applied it to net-next, thanks!
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