Re: [PATCH] perf: ARM_SMMU_V3_PMU should depend on ARM_SMMU_V3

[Geert Uytterhoeven]

Hi Robin,

On Wed, Aug 16, 2023 at 1:23 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> On 2023-08-15 16:36, Geert Uytterhoeven wrote:
> > There is no point in monitoring transactions passing through the SMMU
> > when ARM Ltd. System MMU Version 3 (SMMUv3) Support is disabled.
> > Hence replace the dependency on ARM64 by a dependency on ARM_SMMU_V3
> > (which implies the former).
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > ---
> > This caught my eye after commit 7c3f204e544dfa37 ("perf/smmuv3: Remove
> > build dependency on ACPI") in arm64/for-next/core.
> >
> > Perhaps my understanding is wrong? Is there anything to monitor when
> > ARM_SMMU_V3=n?
>
> Yes, at least TBU event 1 still counts bypass transactions even when the
> SMMU is disabled, so PMCGs can be useful as basic traffic monitors in
> their own right. Plus the original design intent was that PMCGs may also
> be implemented by other things that interact with the SMMU, like
> ATS-capable PCIe root complexes, or devices with their own internal
> TLBs, thus they could potentially count any manner of
> implementation-defined events that aren't necessarily related to SMMU
> translation.

Thanks for the explanation!
Hereby I withdraw my patch.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds