linux-kernel - Re: [PATCH] sched/core: Export pelt_thermal

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Message-ID: <20211028161855.GN174703@worktop.programming.kicks-ass.net>
Date:   Thu, 28 Oct 2021 18:18:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Qais Yousef <qais.yousef@....com>, Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/core: Export pelt_thermal_tp

On Thu, Oct 28, 2021 at 09:00:56AM -0700, Christoph Hellwig wrote:
> On Thu, Oct 28, 2021 at 12:50:05PM +0100, Qais Yousef wrote:
> > We can't use this tracepoint in modules without having the symbol
> > exported first, fix that.
> 
> Which modules is using this?  In linux-next there does not seems to be
> any user outside of kernel/sched/pelt.c.
> 
> > @@ -36,6 +36,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_rt_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp);
> > +EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_thermal_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_cpu_capacity_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
> 
> ... and while we're at it, all these exports are unused and should
> be deleted as well.

This is my concession wrt tracepoints. Actual tracepoints are ABI,
exports are in-kernel interfaces and are explicitly not ABI.

This way people can use an external module to get at the tracepoint data
without having in-tree tracepoints.