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[79.181.137.172]) by smtp.gmail.com with ESMTPSA id g25sm5422740wmk.43.2021.05.05.03.34.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 May 2021 03:34:46 -0700 (PDT) Date: Wed, 5 May 2021 06:34:44 -0400 From: "Michael S. Tsirkin" To: Enrico Granata Cc: virtio-dev@lists.oasis-open.org, hch@infradead.org, linux-block@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH] Provide detailed specification of virtio-blk lifetime metrics Message-ID: <20210505062458-mutt-send-email-mst@kernel.org> References: <20210420162556.217350-1-egranata@google.com> <20210502045740-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210502045740-mutt-send-email-mst@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Sun, May 02, 2021 at 05:12:14AM -0400, Michael S. Tsirkin wrote: > On Tue, Apr 20, 2021 at 04:25:56PM +0000, Enrico Granata wrote: > > In the course of review, some concerns were surfaced about the > > original virtio-blk lifetime proposal, as it depends on the eMMC > > spec which is not open > > > > Add a more detailed description of the meaning of the fields > > added by that proposal to the virtio-blk specification, as to > > make it feasible to understand and implement the new lifetime > > metrics feature without needing to refer to JEDEC's specification > > > > This patch does not change the meaning of those fields nor add > > any new fields, but it is intended to provide an open and more > > clear description of the meaning associated with those fields. > > > > Signed-off-by: Enrico Granata > > Enrico it's great that you are reaching out to the > wider storage community before making spec changes. > > Christoph could you please comment on whether this addresses > your concerns with the lifetime feature. > You wrote "it really needs to stand a lone and be properly documented" > and this seems to be the direction this patch is going in. > > > > --- > > content.tex | 34 +++++++++++++++++++++++++++------- > > 1 file changed, 27 insertions(+), 7 deletions(-) > > > > diff --git a/content.tex b/content.tex > > index 9232d5c..7e14ccc 100644 > > --- a/content.tex > > +++ b/content.tex > > @@ -4669,13 +4669,32 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope > > \end{lstlisting} > > > > The device lifetime metrics \field{pre_eol_info}, \field{device_lifetime_est_a} > > -and \field{device_lifetime_est_b} have the semantics described by the JESD84-B50 > > -specification for the extended CSD register fields \field{PRE_EOL_INFO} > > -\field{DEVICE_LIFETIME_EST_TYP_A} and \field{DEVICE_LIFETIME_EST_TYP_B} > > -respectively. > > +and \field{device_lifetime_est_b} are discussed in the JESD84-B50 specification. > > > > -JESD84-B50 is available at the JEDEC website (https://www.jedec.org) > > -pursuant to JEDEC's licensing terms and conditions. > > +The complete JESD84-B50 is available at the JEDEC website (https://www.jedec.org) > > +pursuant to JEDEC's licensing terms and conditions. > > These links really belong in either normative or non-normative > references section. > > > For the purposes of this > > +specification, these fields are defined as follows. > > All this seems kind of vague. What does one need that spec for? > Is it just a note for pass-through developers? > > How about "to simplify pass-through > from eMMC devices the format of fields > pre_eol_info, device_lifetime_est_typ_a and device_lifetime_est_typ_b > matches PRE_EOL_INFO, DEVICE_LIFETIME_EST_TYP_A and DEVICE_LIFETIME_EST_TYP_B > in the > \hyperref[intro:PCI]{[PCI]}. > > > > Also, now that I mention it, what about NVMe pass-through? Arguably > nvme is getting more popular. Will we be able to support that use-case > as well? Or is more data needed? What is the plan there? > > > + > > +The \field{pre_eol_info} will have one of these values: Besides specifying the values what does it mean exactly? E.g. what are blocks? E.g. "pre_eol_info specifies the percentage of blocks consumed on the device" and explain what blocks are here. > > + > > +\begin{lstlisting} > > +// Value not available > > +#define PRE_EOL_INFO_UNDEFINED 0 > > +// < 80% of blocks are consumed > > +#define PRE_EOL_INFO_NORMAL 1 > > +// 80% of blocks are consumed > > +#define PRE_EOL_INFO_WARNING 2 > > +// 90% of blocks are consumed > > +#define PRE_EOL_INFO_URGENT 3 > > +// All others values are reserved Also please prefix with VIRTIO_BLK_ for consistency. > > > Block comments /* */ should be used as these are documented > in the introduction. > > > +\end{lstlisting} > > + > > +The \field{device_lifetime_est_typ_a} refers to wear of SLC cells and is provided in > > +increments of 10%, with 0 meaning undefined, 1 meaning up-to 10% of lifetime used, and so on, > > +thru to 11 meaning estimated lifetime exceeded. All values above 11 are reserved. > > + > > +The \field{device_lifetime_est_typ_b} refers to wear of MLC cells and is provided with > > +the same semantics as \field{device_lifetime_est_typ_a}. > > > > The final \field{status} byte is written by the device: either > > VIRTIO_BLK_S_OK for success, VIRTIO_BLK_S_IOERR for device or driver > > @@ -4812,7 +4831,8 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope > > or UFS persistent storage), the device SHOULD offer the VIRTIO_BLK_F_LIFETIME > > flag. The flag MUST NOT be offered if the device is backed by storage for which > > the lifetime metrics described in this document cannot be obtained or for which > > -such metrics have no useful meaning. > > +such metrics have no useful meaning. If the metrics are offered, the device MUST NOT > > +send any reserved values, as defined in this specification. > > > > \subsubsection{Legacy Interface: Device Operation}\label{sec:Device Types / Block Device / Device Operation / Legacy Interface: Device Operation} > > When using the legacy interface, transitional devices and drivers > > -- > > 2.31.1.368.gbe11c130af-goog > >