netdev - Re: [PATCH] be2net: Bugfix for packet drop with kernel param swiotlb=force

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Message-ID: <1393033796.15717.90.camel@deadeye.wl.decadent.org.uk>
Date:	Sat, 22 Feb 2014 01:49:56 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Sathya Perla <Sathya.Perla@...lex.Com>
Cc:	"jiang.biao2@....com.cn" <jiang.biao2@....com.cn>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Subramanian Seetharaman <subbu.seetharaman@...lex.com>,
	Ajit Khaparde <Ajit.Khaparde@...lex.Com>,
	"wang.liang82@....com.cn" <wang.liang82@....com.cn>,
	"cai.qu@....com.cn" <cai.qu@....com.cn>,
	"li.fengmao@....com.cn" <li.fengmao@....com.cn>,
	"long.chun@....com.cn" <long.chun@....com.cn>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] be2net: Bugfix for packet drop with kernel param
 swiotlb=force

On Thu, 2014-02-20 at 09:39 +0000, Sathya Perla wrote:
> > -----Original Message-----
> > From: jiang.biao2@....com.cn [mailto:jiang.biao2@....com.cn]
> > 
> > 
> > From: Li Fengmao <li.fengmao@....com.cn>
> > 
> > There will be packet drop with kernel param "swiotlb = force" on
> > Emulex 10Gb NIC using be2net driver. The problem is caused by
> > receiving skb without calling pci_unmap_page() in get_rx_page_info().
> > rx_page_info->last_page_user is initialized to false in
> > be_post_rx_frags() when current frag are mapped in the first half of
> > the same page with another frag. But in that case with
> > "swiotlb = force" param, data can not be copied into the page of
> > rx_page_info without calling pci_unmap_page, so the data frag mapped
> > in the first half of the page will be dropped.
> > 
> > It can be solved by creating only a mapping relation between frag
> > and page, and deleting rx_page_info->last_page_user to ensure
> > calling pci_unmap_page when handling each receiving frag.
> 
> This patch uses an entire page for each RX frag (whose default size is 2048).
> Consequently, on platforms like ppc64 where the default PAGE_SIZE is 64K,
> memory usage becomes very inefficient.
> 
> Instead, I've tried a partial-page mapping scheme. This retains the
> page sharing logic, but un-maps each frag separately so that
> the data is copied from the bounce buffers.
[...]

You don't need to map/unmap each fragment separately; you can sync a
sub-page range with dma_sync_single_for_cpu().

Ben.

-- 
Ben Hutchings
I haven't lost my mind; it's backed up on tape somewhere.

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