Re: [PATCH 0/3] arm_pmu: acpi: avoid allocations in atomic context

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Oct 18, 2022 at 09:53:09PM +0800, Kunkun Jiang wrote:
> Hi Mark:
> 
> On 2022/9/30 19:18, Mark Rutland wrote:
> > I've tested the series in a VM, using ACPI and faked MIDR values to test
> > a few homogeneous and heterogeneous configurations, using the 'maxcpus'
> > kernel argument to test the late-hotplug behaviour:
> I did the same test as you(without this series) and encountered the same
> problem.
> Nice to see this series while asking for help in the community. But why not
> register their own CPU PMU for late hotplugged cpus with a unique MIDR? Are
> there
> any restrictions here?

We can't allcoate memory and so on during the onlining, and generally we
do not expect late hotplug of CPU types that weren't present during
boot (as e.g. errata handling won't work).

Thanks,
Mark.

> 
> Thanks,
> Kunkun Jiang
> > 
> > * On a system where all CPUs have the same MIDR, late-onlining a CPU causes it
> >    to be associated with a matching PMU:
> > 
> >    | # ls /sys/bus/event_source/devices/
> >    | armv8_pmuv3_0  breakpoint     software       tracepoint
> >    | # cat /sys/bus/event_source/devices/armv8_pmuv3_0/cpus
> >    | 0-7
> >    | # echo 1 > /sys/devices/system/cpu/cpu10/online
> >    | Detected PIPT I-cache on CPU10
> >    | GICv3: CPU10: found redistributor a region 0:0x00000000081e0000
> >    | GICv3: CPU10: using allocated LPI pending table @0x00000000402b0000
> >    | CPU10: Booted secondary processor 0x000000000a [0x431f0af1]
> >    | # ls /sys/bus/event_source/devices/
> >    | armv8_pmuv3_0  breakpoint     software       tracepoint
> >    | # cat /sys/bus/event_source/devices/armv8_pmuv3_0/cpus
> >    | 0-7,10
> > 
> > * On a system where all CPUs have a unique MIDR, each of the boot-time
> >    CPUs gets a unique PMU:
> > 
> >    | # ls /sys/bus/event_source/devices/
> >    | armv8_pmuv3_0  armv8_pmuv3_3  armv8_pmuv3_6  software
> >    | armv8_pmuv3_1  armv8_pmuv3_4  armv8_pmuv3_7  tracepoint
> >    | armv8_pmuv3_2  armv8_pmuv3_5  breakpoint
> > 
> > * On a system where all CPUs have a unique MIDR, late-onlining a CPU
> >    results in that CPU not being associated with a PMU, but the CPU is
> >    successfully onlined:
> > 
> >    | # echo 1 > /sys/devices/system/cpu/cpu8/online
> >    | Detected PIPT I-cache on CPU8
> >    | GICv3: CPU8: found redistributor 8 region 0:0x00000000081a0000
> >    | GICv3: CPU8: using allocated LPI pending table @0x0000000040290000
> >    | Unable to associate CPU8 with a PMU
> >    | CPU8: Booted secondary processor 0x0000000008 [0x431f0af1]
> > 
> > Thanks,
> > Mark.
> > 
> > Mark Rutland (3):
> >    arm_pmu: acpi: factor out PMU<->CPU association
> >    arm_pmu: factor out PMU matching
> >    arm_pmu: rework ACPI probing
> > 
> >   drivers/perf/arm_pmu.c       |  17 +-----
> >   drivers/perf/arm_pmu_acpi.c  | 113 ++++++++++++++++++++---------------
> >   include/linux/perf/arm_pmu.h |   1 -
> >   3 files changed, 69 insertions(+), 62 deletions(-)
> > 

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