Re: [PATCH v5 09/11] coresight: etm4x: Add flag to control single-shot restart

On 11/11/2025 10:18, Leo Yan wrote:

On Tue, Nov 11, 2025 at 09:43:13AM +0000, Suzuki Kuruppassery Poulose wrote:

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if (!is_idle_task(current)) {
    if (config->ss_ctrl[i] || config->ss_pe_cmp[i])
        config->ss_status[i] &= ~TRCSSCSRn_STATUS;
}

What happens when we do a system wide session and a CPU is running an idle task ?

For a system wide trace, the ETM device is enabled and disabled by the perf when the session start and finish.

During the session:

• If CPU off states are not enabled, nothing will happen in idle threads, as no CPU PM notifier will be invoked.

What is a CPU is running the idle task, when the system wide session is activated ? Basing our decision to tune the ETM control on the "active task being idle" feels fragile to me. This is purely a decision under ETM driver, specific to the session you are dealing with. Thus having it in the "config" is preferred and is cleaner.

Suzuki

• If CPU off states have been enabled, CPU PM notifier will save and restore ETM device context, and keep single-shot status. This is same with current save/restore flow.

I don't see any issue for this.

Thanks, Leo