Re: [Xen-devel] [PATCH] xen/sched: remove sched_init_pdata()

[Jürgen Groß <jgross@xxxxxxxx>]

On 11.02.20 11:37, Dario Faggioli wrote:
> On Mon, 2020-02-10 at 16:39 +0100, Juergen Gross wrote:
> > sched_init_pdata() is used nowhere, it can be removed. Same applies
> > to
> > the .init_pdata hook of the per-scheduler interface.
> Right, and that appear to be the case since
> f855dd962523b6cb47a92037bdd28b1485141abe ("sched: add minimalistic idle
> scheduler for free cpus"), which removed all call sites.
>
> And that is because switching to a scheduler always happens via
> switch_sched from the idle scheduler, and it's there that we do all the
> initializations, right?
>
> This change is obviously doing the right thing, removing code that is
> never called! :-)
>
> Can we, though:
> - add a mention to the commit above and a quick explanation of things
>    in the changelog?
Okay.

> - update the following comments too:
>    1) in cpu_schedule_callback()
>
> "* This happens by calling the deinit_pdata and free_pdata hooks, in this
>   * order. If no per-pCPU memory was allocated, there is no need to
>   * provide an implementation of free_pdata. deinit_pdata may, however,
>   * be necessary/useful in this case too (e.g., it can undo something done
>   * on scheduler wide data structure during init_pdata). Both deinit_pdata
>   * and free_pdata are called during CPU_DEAD."
>
>    2) schedule_cpu_add()
>
> "*  - a valid instance of per-CPU scheduler specific data, as it is
>   *    allocated by sched_alloc_pdata(). Note that we do not want to
>   *    initialize it yet (i.e., we are not calling sched_init_pdata()).
>   *    That will be done by the target scheduler, in sched_switch_sched(),
>   *    in proper ordering and with locking."
Oh, I missed those. Will modify the comments.


Juergen

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