Re: [PATCH v3 0/5] arm64: SPE ACPI enablement

[Sudeep Holla <sudeep.holla@arm.com>]

On Wed, May 08, 2019 at 05:35:51PM +0800, Hanjun Guo wrote:
> +Cc Alexander.
>
> On 2019/5/8 1:58, Jeremy Linton wrote:
> > Hi,
> >
> > On 5/4/19 6:06 AM, Hanjun Guo wrote:
> >> Hi Jeremy, Mark,
> >>
> >> On 2019/5/4 7:24, Jeremy Linton wrote:
> >>> This patch series enables the Arm Statistical Profiling
> >>> Extension (SPE) on ACPI platforms.
> >>>
> >>> This is possible because ACPI 6.3 uses a previously
> >>> reserved field in the MADT to store the SPE interrupt
> >>> number, similarly to how the normal PMU is described.
> >>> If a consistent valid interrupt exists across all the
> >>> cores in the system, a platform device is registered.
> >>> That then triggers the SPE module, which runs as normal.
> >>>
> >>> We also add the ability to parse the PPTT for IDENTICAL
> >>> cores. We then use this to sanity check the single SPE
> >>> device we create. This creates a bit of a problem with
> >>> respect to the specification though. The specification
> >>> says that its legal for multiple tree's to exist in the
> >>> PPTT. We handle this fine, but what happens in the
> >>> case of multiple tree's is that the lack of a common
> >>> node with IDENTICAL set forces us to assume that there
> >>> are multiple non-IDENTICAL cores in the machine.
> >>
> >> Adding this patch set on top of latest mainline kernel,
> >> and tested on D06 which has the SPE feature, in boot message
> >> shows it was probed successfully:
> >>
> >> arm_spe_pmu arm,spe-v1: probed for CPUs 0-95 [max_record_sz 128, align 4, features 0x7]
> >>
> >> but when I test it with spe events such as
> >>
> >> perf record -c 1024 -e arm_spe_0/branch_filter=0/ -o spe ls
> >>
> >> it fails with:
> >> failed to mmap with 12 (Cannot allocate memory),
> >>
> >> Confirmed that patch [0] is merged and other perf events are working
> >> fine.
> >
> > Its pretty easy to get into the weeds with this driver, does it work with examples like:
> >
> > https://lkml.org/lkml/2018/1/14/122
>
> No, not work at all.
>
> SPE works on 5.0, but not work after 5.1-rc1, bisected to this commit:
>
> 5768402fd9c6 perf/ring_buffer: Use high order allocations for AUX buffers optimistically
>

Indeed this patch breaks SPE. As mentioned in the patch, it uses high
order allocations for AUX buffers and SPE PMU setup_aux explicitly
fails with the warning "unexpected high-order page for auxbuf!" if
it encounters one.

I don't know the intention of that check in SPE. Will ?

--
Regards,
Sudeep