linux-kernel - Re: [PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA

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Message-Id: <b9ae3ee9-1296-4a0d-b6e2-97aaf551482c@app.fastmail.com>
Date: Thu, 12 Jun 2025 17:40:33 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "James Clark" <james.clark@...aro.org>,
 "Vladimir Oltean" <vladimir.oltean@....com>
Cc: "Frank Li" <Frank.li@....com>, "Vladimir Oltean" <olteanv@...il.com>,
 "Mark Brown" <broonie@...nel.org>, linux-spi@...r.kernel.org,
 imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA

On Thu, Jun 12, 2025, at 16:14, James Clark wrote:
> On 12/06/2025 12:15 pm, Vladimir Oltean wrote:
> This leads me to realise a mistake in my original figures. My head was 
> stuck in target mode where we use DMA so I forgot to force DMA in host 
> mode to run the performance tests. The previous figures were all XSPI 
> mode and the small difference in performance could have been just down 
> to the layout of the code changing?
>
> Changing it to DMA mode gives figures that make much more sense:
>
> Coherent (4096 byte transfers): 6534 kbps
> Non-coherent:                   7347 kbps
>
> Coherent (16 byte transfers):    447 kbps
> Non-coherent:                    448 kbps

Ok, good. The improvement from the patch is less than I had hoped
for, but it does sound like at least it doesn't get worse for
small transfers.

     Arnd