linux-kernel - Re: [PATCH linux-next v3 1/1] spi: imx: dynamic burst length adjust for PIO mode

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Message-ID: <592FC889.3020001@mentor.com>
Date:   Thu, 1 Jun 2017 00:55:53 -0700
From:   Jiada Wang <jiada_wang@...tor.com>
To:     Fabio Estevam <festevam@...il.com>
CC:     Mark Brown <broonie@...nel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>
Subject: Re: [PATCH linux-next v3 1/1] spi: imx: dynamic burst length adjust
 for PIO mode

Hello Fabio

On 05/29/2017 04:07 AM, Fabio Estevam wrote:
> Hi Jiada,
>
> On Fri, May 26, 2017 at 2:02 AM,<jiada_wang@...tor.com>  wrote:
>> From: Jiada Wang<jiada_wang@...tor.com>
>>
>> previously burst length (BURST_LENGTH) is always set to equal
>> to bits_per_word, causes a 10us gap between each word in
>> transfer, which significantly affects performance.
>>
>> This patch uses 32 bits transfer to simulate lower bits transfer,
>> and adjusts burst length runtimely to use biggeest burst length
>> as possible to reduce the gaps in transfer for PIO mode.
> Just curious: what is the performance gain you observe with this patch?
I did some performance test with 576/384/192 bytes data,
following is the result between the test w & w/o this patch
(ecspi controller works in PIO and loopback mode)

with this patch:
bytes      bpw      time (ms)
576         8           9.2
576         16         9.2
384         8            6.2
192          8           3.1

without this patch
bytes      bpw      time(ms)
576           8           14.4
576           16          11.6
384           8            9.6
384           16          7.8
192           8            4.8
192           16          3.9


Thanks,
Jiada