From: Jonathan Lemon <jonathan.lemon@gmail.com>
To: "Björn Töpel" <bjorn.topel@gmail.com>
Cc: maximmi@mellanox.com, konrad.wilk@oracle.com,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
davem@davemloft.net, iommu@lists.linux-foundation.org,
bpf@vger.kernel.org, "Björn Töpel" <bjorn.topel@intel.com>,
hch@lst.de, magnus.karlsson@intel.com
Subject: Re: [PATCH net] xsk: remove cheap_dma optimization
Date: Fri, 26 Jun 2020 13:44:48 -0700 [thread overview]
Message-ID: <20200626204448.bxvr35qaxkfj6chs@bsd-mbp> (raw)
In-Reply-To: <20200626134358.90122-1-bjorn.topel@gmail.com>
On Fri, Jun 26, 2020 at 03:43:58PM +0200, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@intel.com>
>
> When the AF_XDP buffer allocation API was introduced it had an
> optimization, "cheap_dma". The idea was that when the umem was DMA
> mapped, the pool also checked whether the mapping required a
> synchronization (CPU to device, and vice versa). If not, it would be
> marked as "cheap_dma" and the synchronization would be elided.
>
> In [1] Christoph points out that the optimization above breaks the DMA
> API abstraction, and should be removed. Further, Christoph points out
> that optimizations like this should be done within the DMA mapping
> core, and not elsewhere.
>
> Unfortunately this has implications for the packet rate
> performance. The AF_XDP rxdrop scenario shows a 9% decrease in packets
> per second.
>
> [1] https://lore.kernel.org/netdev/20200626074725.GA21790@lst.de/
>
> Cc: Christoph Hellwig <hch@lst.de>
> Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API")
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
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next prev parent reply other threads:[~2020-06-26 20:56 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-26 13:43 [PATCH net] xsk: remove cheap_dma optimization Björn Töpel
2020-06-26 20:44 ` Jonathan Lemon [this message]
2020-06-26 23:00 ` Daniel Borkmann
2020-06-27 7:04 ` Christoph Hellwig
2020-06-28 17:16 ` Björn Töpel
2020-06-29 13:52 ` Daniel Borkmann
2020-06-29 15:10 ` Björn Töpel
2020-06-29 15:18 ` Daniel Borkmann
2020-06-29 16:23 ` Björn Töpel
2020-06-30 5:07 ` Christoph Hellwig
2020-06-30 13:47 ` Daniel Borkmann
2020-06-29 15:41 ` Robin Murphy
2020-07-01 10:17 ` Björn Töpel
2020-07-08 6:50 ` Christoph Hellwig
2020-07-08 7:57 ` Song Bao Hua (Barry Song)
2020-07-08 12:19 ` Christoph Hellwig
2020-07-08 13:18 ` Robin Murphy
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