linux-kernel - Re: [RFC] Signaling overhead on RT tasks is causing RCU stall

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Message-ID: <20240709074333.2799005-2-radoslaw.zielonek@gmail.com>
Date: Tue,  9 Jul 2024 09:43:34 +0200
From: Radoslaw Zielonek <radoslaw.zielonek@...il.com>
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Subject: Re: [RFC] Signaling overhead on RT tasks is causing RCU stall

> I'm having trouble parsing this. What overhead becomes high? Is the task
> spending time in-kernel? Because if the task is spending time in-user
> handling all its signals, it should accumulate runtime just fine.

The overhead is in kernel. The RT task is preempted over and over by SIGRETURN.

In my case userspace set posix timer interval to 8ns.
The posix_timer_fn enqueues signal (send_sigqueue).
Then when the signal is dequeued (dequeue_signal) the posix timer is rearmed.

Radoslaw