Re: [PATCH 0/1] arm64: defconfig: Add Coresight as module

Catalin Marinas
2022-09-22T10:53:00Z

On Thu, Sep 22, 2022 at 10:34:45AM +0100, James Clark wrote:
> On 21/09/2022 16:08, Catalin Marinas wrote:
> > 2. Always on CONFIG_PID_IN_CONTEXTIDR (we might as well remove the
> > Kconfig entry). This would write the root pid namespace value
> > (task_pid_nr()).
>
> If we're not worried about the overhead after all, this would be the
> easiest solution. And then SPE or Coresight already decide whether they
> want to use the value or not, so no further changes are needed.
>
> From Leo's patch there is a table that shows a 1% overhead with it
> enabled permanently, and I've heard a figure like that mentioned before.
> So I could also resurrect that patch to use static keys? Although it's a
> bit more complicated, that would be my preference. And then we can have
> that mode always on.

I don't think we should bother with static keys, just always enable it
but try to reduce/group the ISBs from all the functions called on the
__switch_to() path. We may actually get a speed-up.

--
Catalin