linux-kernel - Re: [PATCH v2] trace: Add migrate-disabled counter to tracing output.

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Date:   Tue, 7 Sep 2021 11:21:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] trace: Add migrate-disabled counter to tracing
 output.

On Mon, 6 Sep 2021 10:13:43 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> I left that with that XXX on purpose so you can look and comment and say
> how to fix it. The problem I had with preempt_count was that only the
> lower nibble contains the preemption counter. So I thought you could
> easily came up with something how this can be split or taught to only
> expose the lower nibble. I didn't after a few attempts.
> My understanding is that this `preempt_count' is also used in the filter
> tracefs file so something like "preempt_count > 1" > filter would also
> match for migrate_count = 2, preempt_count = 1. You seem to be happy to
> filter in user space.

Right. It will break filtering, and I don't see a good way to handle that.

That said, I'll update the code to handle comparing fields with a mask.
I'll need to do this with the kernel as well.

I'm fine with breaking the filtering on preempt_count over having it just
fail to print it at all.

-- Steve