linux-kernel - RE: [PATCH v6 0/6] Support hld delayed init based on Pseudo-NMI for arm64

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Date:   Wed, 13 Jul 2022 18:38:14 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <lecopzer.chen@...iatek.com>
CC:     <acme@...nel.org>, <akpm@...ux-foundation.org>,
        <alexander.shishkin@...ux.intel.com>, <catalin.marinas@....com>,
        <davem@...emloft.net>, <jolsa@...hat.com>, <jthierry@...hat.com>,
        <keescook@...omium.org>, <kernelfans@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>, <mark.rutland@....com>,
        <masahiroy@...nel.org>, <matthias.bgg@...il.com>, <maz@...nel.org>,
        <mcgrof@...nel.org>, <mingo@...hat.com>, <namhyung@...nel.org>,
        <nixiaoming@...wei.com>, <peterz@...radead.org>,
        <pmladek@...e.com>, <sparclinux@...r.kernel.org>,
        <sumit.garg@...aro.org>, <wangqing@...o.com>, <will@...nel.org>,
        <yj.chiang@...iatek.com>
Subject: RE: [PATCH v6 0/6] Support hld delayed init based on Pseudo-NMI for arm64

Hi Will, Mark
 
Sorry for another ping,
but would you please help review this 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/
> 
>