linux-kernel - Re: [BUG] - Short freezes in gameplay due to MMC_CAP_AGGRESSIVE

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Message-ID: <0b6fd99b-54a6-45f1-942e-94f707f2fbf5@acm.org>
Date: Wed, 28 Jan 2026 09:14:36 -0800
From: Bart Van Assche <bvanassche@....org>
To: Ulf Hansson <ulf.hansson@...aro.org>, Christoph Hellwig <hch@....de>,
 Jens Axboe <axboe@...nel.dk>, Ricky WU <ricky_wu@...ltek.com>,
 Matthew Schwartz <matthew.schwartz@...ux.dev>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
 linux-block <linux-block@...r.kernel.org>
Subject: Re: [BUG] - Short freezes in gameplay due to MMC_CAP_AGGRESSIVE_PM on
 RTS525A card reader

On 1/28/26 5:23 AM, Ulf Hansson wrote:
> How does other block device drivers do this?

The role of the Linux kernel is to provide mechanisms while remaining as
policy-neutral as possible. In other words, it is up to user space to
decide whether to enable or to disable runtime PM.

For UFS devices some form of runtime PM is enabled by default for
battery-powered devices because otherwise the impact on battery life
would be unacceptable. If the latency impact of runtime resume is not
acceptable for some applications then it is up to user space software to
tune runtime power management as necessary.

Additionally, cpu_latency_qos_update_request() is called by the UFS
driver during runtime suspend and resume to prevent that CPU frequency
scaling negatively affects UFS processing latency. I'd like to move
these cpu_latency_qos_update_request() calls from the UFS driver into
the block layer core because I think that every block driver that
supports runtime power management needs this.

Bart.