linux-kernel - Re: [PATCH v2 3/4] ASoC: fsl: fsl_qmc_audio: Only request completion on last channel

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Message-ID: <20250813120703.6e8eed30@bootlin.com>
Date: Wed, 13 Aug 2025 12:07:03 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Qiang Zhao <qiang.zhao@....com>, Shengjiu Wang
 <shengjiu.wang@...il.com>, Xiubo Li <Xiubo.Lee@...il.com>, Fabio Estevam
 <festevam@...il.com>, Nicolin Chen <nicoleotsuka@...il.com>, Liam Girdwood
 <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, Jaroslav Kysela
 <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org
Subject: Re: [PATCH v2 3/4] ASoC: fsl: fsl_qmc_audio: Only request
 completion on last channel

On Tue, 12 Aug 2025 12:50:57 +0200
Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> In non-interleaved mode, several QMC channels are used in sync.
> More details can be found in commit 188d9cae5438 ("ASoC: fsl:
> fsl_qmc_audio: Add support for non-interleaved mode.")
> At the time being, an interrupt is requested on each channel to
> perform capture/playback completion, allthough the completion is
> really performed only once all channels have completed their work.
> 
> This leads to a lot more interrupts than really needed. Looking at
> /proc/interrupts shows ~3800 interrupts per second when using
> 4 capture and 4 playback devices with 5ms periods while
> only 1600 (200 x 4 + 200 x 4) periods are processed during one second.
> 
> The QMC channels work in sync, the one started first is the one
> finishing first and the one started last is the one finishing last,
> so when the last one finishes it is guaranteed that the other ones are
> finished as well. Therefore only request completion processing on the
> last QMC channel.
> 
> On my board with the above exemple, on a kernel started with
> 'threadirqs' option, the QMC irq thread uses 16% CPU time with this
> patch while it uses 26% CPU time without this patch.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  sound/soc/fsl/fsl_qmc_audio.c | 46 +++++------------------------------
>  1 file changed, 6 insertions(+), 40 deletions(-)
> 

Acked-by: Herve Codina <herve.codina@...tlin.com>

Best regards,
Hervé



-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com