linux-kernel - Re: [PATCH 1/3] spi: spi-xilinx: Remove ISR race condition

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Message-ID: <CAKfKVtF8d5Q0eond4X1zctUbLS4XEnbRMYmoQjuVfHBXKQby1Q@mail.gmail.com>
Date:	Fri, 4 Dec 2015 10:52:56 +0530
From:	Shubhrajyoti Datta <shubhrajyoti.datta@...il.com>
To:	Jean-Francois Dagenais <jeff.dagenais@...il.com>
Cc:	Mark Brown <broonie@...nel.org>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, Michal Simek <monstr@...str.eu>,
	Peter Crosthwaite <pcrost@...inx.com>,
	Peter Crosthwaite <peter.crosthwaite@...alogix.com>,
	Grant Likely <grant.likely@...aro.org>,
	spi-devel-general@...ts.sourceforge.net,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/3] spi: spi-xilinx: Remove ISR race condition

>
>>
>> =============
>> spi: xilinx - minimize iomem reads
>>
>>     If this IP core is accessed through bridges like PCI-e, reads are rather
>>     costly. Doing many reads or read-modify-writes is thus long and strenuous
>>     on the CPU (active waiting).
>>
>>     The transfer workflow of this driver allows some assumptions to be made and
>>     exploited to minimize reads as much as possible.
>>
>>     These two assumptions are made:
>>     - since we are in control of the CR register, cache it so we don't have to
>>       read it all the time to modify it.
>
> Makes sense.

I have made an attempt at it can you check if you get any performance
improvemets
on your setup.

http://www.spinics.net/lists/linux-spi/msg05963.html


Thanks,
Shubhrajyoti
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