linux-kernel - Re: [PATCH 0/9] IB: Optimize DMA mapping

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Date:   Tue, 10 Jan 2017 17:28:14 -0800
From:   "santosh.shilimkar@...cle.com" <santosh.shilimkar@...cle.com>
To:     Bart Van Assche <bart.vanassche@...disk.com>,
        Doug Ledford <dledford@...hat.com>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9] IB: Optimize DMA mapping

On 1/10/17 4:56 PM, Bart Van Assche wrote:
> Hello Doug,
>
> As you know there are two sets of DMA mapping operations in the Linux
> kernel:
> - One set of DMA mapping operations that is used by most drivers.
> - Another set of DMA mapping operations that is only used by the RDMA
>   drivers.
> Having two sets of DMA mapping operations is not only a source of
> confusion but also a source of unnecessary overhead. The DMA mapping
> operations are in the hot path so it is important that the overhead
> of these operations is as low as possible. Hence this patch series
> that converts the RDMA code to the standard DMA mapping API and
> thereby eliminates the if (dev->dma_ops) test from the hot path. An
> additional benefit is that the size of HW and SW drivers that do not
> use DMA is reduced by switching to dma_virt_ops.
>
This is really good series. I was always wondering why the extra
indirection was added first place on streaming APIs.

Regards,
Santosh