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From: David Laight <David.Laight@ACULAB.COM>
To: 'Alexander Duyck' <alexander.duyck@gmail.com>,
	Govindarajulu Varadarajan <_govind@gmx.com>,
	Alexander Duyck <alexander.h.duyck@redhat.com>
Cc: "davem@davemloft.net" <davem@davemloft.net>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"ssujith@cisco.com" <ssujith@cisco.com>,
	"benve@cisco.com" <benve@cisco.com>
Subject: RE: [PATCH net-next v3 2/2] enic: use netdev_dma_alloc
Date: Wed, 11 Mar 2015 17:34:23 +0000	[thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CAFB899@AcuExch.aculab.com> (raw)
In-Reply-To: <55004A73.3040904@gmail.com>

From: Alexander Duyck
...
> > Is this behaviour platform dependent? I tested this patch for more
> > than a month
> > and I did not face any issue. I ran normal traffic like ssh, nfs and
> > iperf/netperf.
> > Is there a special scenario when this could occur?
> 
> Yes it depends on the platform and IOMMU used.  For an example take a
> loot at the SWIOTLB implementation.  I always assumed if I can work with
> that when it is doing bounce buffers I can work with any IOMMU or platform.
> 
> >
> > Will using DMA_BIDIRECTIONAL and sync_to_cpu & sync_to_device solve this?
> > Each desc should have different dma address to write to. Can you
> > explain me how
> > this can happen?
> 
> No that won't help.  The issue is that when the page is mapped you
> should not be updating any fields in the page until it is unmapped.
> Since you have multiple buffers mapped to a single page you should be
> waiting until the entire page is unmapped.

Isn't the 'unit of memory for dma sync' a cache line, not a page?

You certainly need to test on systems without cache coherent io.

	David

  reply	other threads:[~2015-03-11 17:35 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-10 17:43 [PATCH net-next v3 0/2] introduce dma frag allocation and reduce dma mapping Govindarajulu Varadarajan
2015-03-10 17:43 ` [PATCH net-next v3 1/2] net: implement dma cache skb allocator Govindarajulu Varadarajan
2015-03-10 20:33   ` Alexander Duyck
2015-03-11  8:57     ` Govindarajulu Varadarajan
2015-03-11 13:55       ` Alexander Duyck
2015-03-11 15:42         ` Eric Dumazet
2015-03-11 17:06     ` David Laight
2015-03-14 20:08   ` Ben Hutchings
2015-03-10 17:43 ` [PATCH net-next v3 2/2] enic: use netdev_dma_alloc Govindarajulu Varadarajan
2015-03-10 20:14   ` Alexander Duyck
2015-03-11  9:27     ` Govindarajulu Varadarajan
2015-03-11 14:00       ` Alexander Duyck
2015-03-11 17:34         ` David Laight [this message]
2015-03-11 17:51           ` Alexander Duyck

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