linux-kernel - Re: [alsa-devel] [PATCH] ASoC: core: Don't schedule DAPM work if already in target state

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Date:   Tue, 28 Aug 2018 11:39:11 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Jon Hunter <jonathanh@...dia.com>
CC:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, <linux-tegra@...r.kernel.org>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH] ASoC: core: Don't schedule DAPM work if
 already in target state

On Fri, Aug 17, 2018 at 04:35:43PM +0100, Jon Hunter wrote:
> When dapm_power_widgets() is called, the dapm_pre_sequence_async() and
> dapm_post_sequence_async() functions are scheduled for all DAPM contexts
> (apart from the card DAPM context) regardless of whether the DAPM
> context is already in the desired state. The overhead of this is not
> insignificant and the more DAPM contexts there are the more overhead
> there is.
> 
> For example, on the Tegra124 Jetson TK1, when profiling the time taken
> to execute the dapm_power_widgets() the following times were observed.
> 
>   Times for function dapm_power_widgets() are (us):
>      Min 23, Ave 190, Max 434, Count 39
> 
> Here 'Count' is the number of times that dapm_power_widgets() has been
> called. Please note that the above time were measured using ktime_get()
> to log the time on entry and exit from dapm_power_widgets(). So it
> should be noted that these times may not be purely the time take to
> execute this function if it is preempted. However, after applying this
> patch and measuring the time taken to execute dapm_power_widgets() again
> a significant improvement is seen as shown below.
> 
>   Times for function dapm_power_widgets() are (us):
>      Min 4, Ave 16, Max 82, Count 39
> 
> Therefore, optimise the dapm_power_widgets() function by only scheduling
> the dapm_pre/post_sequence_async() work if the DAPM context is not in
> the desired state.
> 
> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> ---

Looks ok to me:

Reviewed-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Although that said the performance increase is pretty hard to
measure on my systems.

Thanks,
Charles