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From:   Lecopzer Chen <lecopzer.chen@mediatek.com>
To:     <mark.rutland@arm.com>, <will@kernel.org>
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Subject: RE: [PATCH v7 0/6] Support hld delayed init based on Pseudo-NMI for arm64
Date:   Sat, 3 Sep 2022 17:45:23 +0800
Message-ID: <20220903094523.16002-1-lecopzer.chen@mediatek.com>
In-Reply-To: <20220903093415.15850-1-lecopzer.chen@mediatek.com>
References: <20220903093415.15850-1-lecopzer.chen@mediatek.com>
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Hi Will, Mark
 
Sorry for bothering you, this need to be reviewed by ARM Perf maintainer,

could you please help review this pathset or comment about it?


Thanks a lot.

 
> Hi Will, Mark
>
> Could you help review arm parts of this patchset, please?
> 
> For the question mention in both [1] and [2],
> 
> > I'd still like Mark's Ack on this, as the approach you have taken doesn't
> > really sit with what he was suggesting.
> >
> > I also don't understand how all the CPUs get initialised with your patch,
> > since the PMU driver will be initialised after SMP is up and running.
> 
> The hardlock detector utilizes the softlockup_start_all() to start all
> the cpu on watchdog_allowed_mask, which will do watchdog_nmi_enable()
> that registers perf event on each CPUs.
> Thus we simply need to retry lockup_detector_init() in a single cpu which
> will reconfig and call to softlockup_start_all().
> 
> Also, the CONFIG_HARDLOCKUP_DETECTOR_PERF selects SOFTLOCKUP_DETECTOR,
> IMO, this shows that hardlockup detector supports from softlockup.
> 
> 
> > We should know whether pNMIs are possible once we've completed
> > setup_arch() (and possibly init_IRQ()), long before SMP, so so I reckon
> > we should have all the information available once we get to
> > lockup_detector_init(), even if that requires some preparatory rework.
> 
> Hardlockup depends on PMU driver , I think the only way is moving
> pmu driver at setup_arch() or any point which is earlier than
> lockup_detector_init(), and I guess we have to reorganize the architecture
> of arm PMU.
> 
> The retry function should benifit all the arch/ not only for arm64.
> Any arch who needs to probe its pmu as module can use this without providing
> a chance to mess up the setup order. 
> 
> 
> Please let me know if you have any concern about this, thank you
> 
> 
> [1] https://lore.kernel.org/all/CAFA6WYPPgUvHCpN5=EpJ2Us5h5uVWCbBA59C-YwYQX2ovyVeEw@mail.gmail.com/
> [2] https://lore.kernel.org/linux-arm-kernel/20210419170331.GB31045@willie-the-truck/
> 
>