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Re: [PATCH 3/9] hw/block/nvme: support per-namespace smart log


From: Keith Busch
Subject: Re: [PATCH 3/9] hw/block/nvme: support per-namespace smart log
Date: Thu, 1 Oct 2020 10:30:43 -0700

On Thu, Oct 01, 2020 at 07:18:37PM +0200, Klaus Jensen wrote:
> OK, so I agree that it makes sense for it to be supported on a per
> namespace basis, but I think the spec is just keeping the door open for
> future namespace specific stuff in the log page - currently there is
> none.
> 
> Figure 94 (the actual SMART log page) says that the Data Units
> Read/Written are controller wide, so there really is no namespace
> specific information. Maybe this could be in the context of shared
> namespaces? How would a controller know how much data has been
> read/written from it without asking the other controllers? What if a
> controller is detached from the namespace - you'd lose those numbers.

That text is wrong. There is no "controller" scope to the smart log.
Figure 191 says the smart scope is to the subsystem or the namespace. It
doesn't matter which controller performed an IO to a particular
namespace; the log needs to report the same information regardless of
which controller you query. How that is coordinated within the subsystem
is a detail not defined by spec.

Not that that particular detail matters here, as we don't support
multi-controller subsystems (yet!). But the smart log text has missed an
update to reflect this, so it looks like trivial ECN material to me.



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