From: David Miller <davem@davemloft.net>
To: David.Laight@ACULAB.COM
Cc: ttoukan.linux@gmail.com, edumazet@google.com, brouer@redhat.com,
alexander.duyck@gmail.com, netdev@vger.kernel.org,
tariqt@mellanox.com, kafai@fb.com, saeedm@mellanox.com,
willemb@google.com, bblanco@plumgrid.com, ast@kernel.org,
eric.dumazet@gmail.com, linux-mm@kvack.org
Subject: Re: [PATCH v3 net-next 08/14] mlx4: use order-0 pages for RX
Date: Tue, 14 Feb 2017 12:22:31 -0500 (EST) [thread overview]
Message-ID: <20170214.122231.2022548659001388286.davem@davemloft.net> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6DCFE63512@AcuExch.aculab.com>
From: David Laight <David.Laight@ACULAB.COM>
Date: Tue, 14 Feb 2017 17:17:22 +0000
> From: David Miller
>> Sent: 14 February 2017 17:04
> ...
>> One path I see around all of this is full integration. Meaning that
>> we can free pages into the page allocator which are still DMA mapped.
>> And future allocations from that device are prioritized to take still
>> DMA mapped objects.
> ...
>
> For systems with 'expensive' iommu has anyone tried separating the
> allocation of iommu resource (eg page table slots) from their
> assignment to physical pages?
>
> Provided the page sizes all match, setting up a receive buffer might
> be as simple as writing the physical address into the iommu slot
> that matches the ring entry.
>
> Or am I thinking about hardware that is much simpler than real life?
You still will eat an expensive MMIO or hypervisor call to setup the
mapping.
IOMMU is expensive because of two operations, the slot allocation
(which takes locks) and the modification of the IOMMU PTE to setup
or teardown the mapping.
This is why attempts to preallocate slots (which people have looked
into) never really takes off. You really have to eliminate the
entire operation to get worthwhile gains.
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next prev parent reply other threads:[~2017-02-14 17:22 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-13 19:58 [PATCH v3 net-next 00/14] mlx4: order-0 allocations and page recycling Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 01/14] mlx4: use __skb_fill_page_desc() Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 02/14] mlx4: dma_dir is a mlx4_en_priv attribute Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 03/14] mlx4: remove order field from mlx4_en_frag_info Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 04/14] mlx4: get rid of frag_prefix_size Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 05/14] mlx4: rx_headroom is a per port attribute Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 06/14] mlx4: reduce rx ring page_cache size Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 07/14] mlx4: removal of frag_sizes[] Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 08/14] mlx4: use order-0 pages for RX Eric Dumazet
2017-02-13 20:51 ` Alexander Duyck
2017-02-13 21:09 ` Eric Dumazet
2017-02-13 23:16 ` Alexander Duyck
2017-02-13 23:22 ` Eric Dumazet
2017-02-13 23:26 ` Alexander Duyck
2017-02-13 23:29 ` Eric Dumazet
2017-02-13 23:47 ` Alexander Duyck
2017-02-14 0:22 ` Eric Dumazet
2017-02-14 0:34 ` Alexander Duyck
2017-02-14 0:46 ` Eric Dumazet
2017-02-14 0:47 ` Eric Dumazet
2017-02-14 0:57 ` Eric Dumazet
2017-02-14 1:32 ` Alexander Duyck
2017-02-14 12:12 ` Jesper Dangaard Brouer
2017-02-14 13:45 ` Eric Dumazet
2017-02-14 14:12 ` Eric Dumazet
2017-02-14 14:56 ` Tariq Toukan
2017-02-14 15:51 ` Eric Dumazet
2017-02-14 16:03 ` Eric Dumazet
2017-02-14 17:29 ` Tom Herbert
2017-02-15 16:42 ` Tariq Toukan
2017-02-15 16:57 ` Eric Dumazet
2017-02-16 13:08 ` Tariq Toukan
2017-02-16 15:47 ` Eric Dumazet
2017-02-16 17:05 ` Tom Herbert
2017-02-16 17:11 ` Eric Dumazet
2017-02-16 20:49 ` Saeed Mahameed
2017-02-16 19:03 ` David Miller
2017-02-16 21:06 ` Saeed Mahameed
2017-02-14 17:04 ` David Miller
2017-02-14 17:17 ` David Laight
2017-02-14 17:22 ` David Miller [this message]
2017-02-14 19:38 ` Jesper Dangaard Brouer
2017-02-14 19:59 ` David Miller
2017-02-14 17:29 ` Alexander Duyck
2017-02-14 18:46 ` Jesper Dangaard Brouer
2017-02-14 19:02 ` Eric Dumazet
2017-02-14 20:02 ` Jesper Dangaard Brouer
2017-02-14 21:56 ` Eric Dumazet
2017-02-14 19:06 ` Alexander Duyck
2017-02-14 19:50 ` Jesper Dangaard Brouer
2017-02-22 16:22 ` Eric Dumazet
2017-02-22 17:23 ` Alexander Duyck
2017-02-22 17:58 ` David Laight
2017-02-22 18:21 ` Eric Dumazet
2017-02-23 1:08 ` Alexander Duyck
2017-02-23 2:06 ` Eric Dumazet
2017-02-23 2:18 ` Alexander Duyck
2017-02-23 14:02 ` Tariq Toukan
2017-02-24 9:42 ` Jesper Dangaard Brouer
2017-03-12 14:57 ` Eric Dumazet
2017-03-12 15:29 ` Eric Dumazet
2017-03-12 15:49 ` Saeed Mahameed
2017-03-12 16:49 ` Eric Dumazet
2017-03-13 9:20 ` Saeed Mahameed
2017-02-13 19:58 ` [PATCH v3 net-next 09/14] mlx4: add page recycling in receive path Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 10/14] mlx4: add rx_alloc_pages counter in ethtool -S Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 11/14] mlx4: do not access rx_desc from mlx4_en_process_rx_cq() Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 12/14] mlx4: factorize page_address() calls Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 13/14] mlx4: make validate_loopback() more generic Eric Dumazet
2017-02-13 19:58 ` [PATCH v3 net-next 14/14] mlx4: remove duplicate code in mlx4_en_process_rx_cq() Eric Dumazet
2017-02-17 16:00 ` [PATCH v3 net-next 00/14] mlx4: order-0 allocations and page recycling David Miller
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