linux-kernel - Re: [PATCH v15,RESEND 22/23] PCI: starfive: Offload the NVMe timeout workaround to host drivers.

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Date: Wed, 13 Mar 2024 21:39:34 -0600
From: Keith Busch <kbusch@...nel.org>
To: Kevin Xie <kevin.xie@...rfivetech.com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Minda Chen <minda.chen@...rfivetech.com>,
	Conor Dooley <conor@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"daire.mcnamara@...rochip.com" <daire.mcnamara@...rochip.com>,
	"emil.renner.berthing@...onical.com" <emil.renner.berthing@...onical.com>,
	"krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	"aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	Mason Huo <mason.huo@...rfivetech.com>,
	Leyfoon Tan <leyfoon.tan@...rfivetech.com>
Subject: Re: [PATCH v15,RESEND 22/23] PCI: starfive: Offload the NVMe timeout
 workaround to host drivers.

On Wed, Mar 13, 2024 at 08:51:29PM -0600, Keith Busch wrote:
> I suppose we could quirk a non-posted transaction in the interrupt
> handler to force flush pending memory updates, but that will noticeably
> harm your nvme performance. Maybe if you constrain such behavior to the
> spurious IRQ_NONE condition, then it might be okay? I don't know.

Hm, that may not be good enough: if nvme completions can be reordered
with their msi's, then I assume data may reorder with their completion.
Your application will inevitably see stale and corrupted data, so it
sounds like you need some kind of barrier per completion. Ouch!