linux-kernel - RE: [PATCH v7 0/6] Support hld delayed init based on Pseudo-NMI for arm64

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Message-ID: <20220903094523.16002-1-lecopzer.chen@mediatek.com>
Date:   Sat, 3 Sep 2022 17:45:23 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <mark.rutland@....com>, <will@...nel.org>
CC:     <lecopzer.chen@...iatek.com>, <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-perf-users@...r.kernel.org>,
        <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>,
        <yj.chiang@...iatek.com>
Subject: RE: [PATCH v7 0/6] Support hld delayed init based on Pseudo-NMI for arm64

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/
> 
>