linux-kernel - Re: [PATCH] i2c: imx: use usleep_range(50,100) instead of udelay(50)

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Message-ID: <20160426213527.GI4587@katana>
Date:	Tue, 26 Apr 2016 23:35:27 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Dirk Behme <dirk.behme@...bosch.com>
Cc:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oleksij Rempel <linux@...pel-privat.de>
Subject: Re: [PATCH] i2c: imx: use usleep_range(50,100) instead of udelay(50)

On Tue, Apr 26, 2016 at 08:27:46AM +0200, Dirk Behme wrote:
> From: Oleksij Rempel <linux@...pel-privat.de>
> 
> Documentation/timers/timers-howto.txt recommends to use
> usleep_range on delays > 10usec. According to my test results
> with Neonode zForce touchscreen driver, usleep_range indeed
> reduces CPU load.
> 
> Stats collected with "./perf record -a -g -F 1000 sleep 10"
> 
> i2c-imx with udelay(50):
> 34.19% 0.00% irq/220-Neonode [kernel.kallsyms] [k] irq_thread
>     ---irq_thread
>        |--33.75%--irq_thread_fn
>        |    |--19.27%--0x7f08a878
>        |    |     i2c_master_recv
>        |    |     i2c_transfer
>        |    |     __i2c_transfer
>        |    |     i2c_imx_xfer
>        |    |     |--11.71%--i2c_imx_trx_complete

Reworded $subject to match code and applied to for-next, thanks!


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