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Date: Fri, 10 May 2019 10:23:11 +0200 From: "Rafael J. Wysocki" <rafael@...nel.org> To: Kai-Heng Feng <kai.heng.feng@...onical.com> Cc: Mario Limonciello <Mario.Limonciello@...l.com>, Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...com>, Sagi Grimberg <sagi@...mberg.me>, "Rafael J. Wysocki" <rafael@...nel.org>, Linux PM <linux-pm@...r.kernel.org>, Rafael Wysocki <rafael.j.wysocki@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-nvme <linux-nvme@...ts.infradead.org>, Keith Busch <keith.busch@...el.com> Subject: Re: [PATCH] nvme-pci: Use non-operational power state instead of D3 on Suspend-to-Idle On Fri, May 10, 2019 at 8:08 AM Kai-Heng Feng <kai.heng.feng@...onical.com> wrote: > > at 06:19, <Mario.Limonciello@...l.com> <Mario.Limonciello@...l.com> wrote: > > >> -----Original Message----- > >> From: Keith Busch <kbusch@...nel.org> > >> Sent: Thursday, May 9, 2019 4:54 PM > >> To: Limonciello, Mario > >> Cc: kai.heng.feng@...onical.com; hch@....de; axboe@...com; > >> sagi@...mberg.me; rafael@...nel.org; linux-pm@...r.kernel.org; > >> rafael.j.wysocki@...el.com; linux-kernel@...r.kernel.org; linux- > >> nvme@...ts.infradead.org; keith.busch@...el.com > >> Subject: Re: [PATCH] nvme-pci: Use non-operational power state instead > >> of D3 on > >> Suspend-to-Idle > >> > >> > >> [EXTERNAL EMAIL] > >> > >> On Thu, May 09, 2019 at 09:37:58PM +0000, Mario.Limonciello@...l.com > >> wrote: > >>>> +int nvme_set_power(struct nvme_ctrl *ctrl, unsigned npss) > >>>> +{ > >>>> + int ret; > >>>> + > >>>> + mutex_lock(&ctrl->scan_lock); > >>>> + nvme_start_freeze(ctrl); > >>>> + nvme_wait_freeze(ctrl); > >>>> + ret = nvme_set_features(ctrl, NVME_FEAT_POWER_MGMT, npss, NULL, 0, > >>>> + NULL); > >>>> + nvme_unfreeze(ctrl); > >>>> + mutex_unlock(&ctrl->scan_lock); > >>>> + > >>>> + return ret; > >>>> +} > >>>> +EXPORT_SYMBOL_GPL(nvme_set_power); > >>> > >>> I believe without memory barriers at the end disks with HMB this will > >>> still kernel panic (Such as Toshiba BG3). > >> > >> Well, the mutex has an implied memory barrier, but your HMB explanation > >> doesn't make much sense to me anyway. The "mb()" in this thread's original > >> patch is a CPU memory barrier, and the CPU had better not be accessing > >> HMB memory. Is there something else going on here? > > > > Kai Heng will need to speak up a bit in his time zone as he has this disk > > on hand, > > but what I recall from our discussion was that DMA operation MemRd after > > resume was the source of the hang. > > Yes, that’ what I was told by the NVMe vendor, so all I know is to impose a > memory barrier. > If mb() shouldn’t be used here, what’s the correct variant to use in this > context? > > > > >>> This still allows D3 which we found at least failed to go into deepest > >>> state and > >> blocked > >>> platform s0ix for the following SSDs (maybe others): > >>> Hynix PC601 > >>> LiteOn CL1 > >> > >> We usually write features to spec first, then quirk non-compliant > >> devices after. > > > > NVME spec doesn't talk about a relationship between SetFeatures w/ > > NVME_FEAT_POWER_MGMGT and D3 support, nor order of events. > > > > This is why we opened a dialog with storage vendors, including > > contrasting the behavior > > of Microsoft Windows inbox NVME driver and Intel's Windows RST driver. > > > > Those two I mention that come to mind immediately because they were most > > recently > > tested to fail. Our discussion with storage vendors overwhelmingly > > requested > > that we don't use D3 under S2I because their current firmware > > architecture won't > > support it. > > > > For example one vendor told us with current implementation that receiving > > D3hot > > after NVME shutdown will prevent being able to enter L1.2. D3hot entry > > was supported > > by an IRQ handler that isn't serviced in NVME shutdown state. > > > > Another vendor told us that with current implementation it's impossible > > to transition > > to PS4 (at least via APST) while L1.2 D3hot is active. > > I tested the patch from Keith and it has two issues just as simply skipping > nvme_dev_disable(): > 1) It consumes more power in S2I > 2) System freeze after resume Well, the Keith's patch doesn't prevent pci_pm_suspend_noirq() from asking for D3 and both of the symptoms above may be consequences of that in principle.
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