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Subject: Re: [virtio-dev] [PATCH v3] Add lifetime metrics to virtio-blk
On Wed, 3 Mar 2021 11:01:50 -0700 Enrico Granata <egranata@google.com> wrote: > On Wed, Mar 3, 2021 at 10:18 AM Cornelia Huck <cohuck@redhat.com> wrote: > > > > On Mon, 1 Mar 2021 10:51:03 -0700 > > Enrico Granata <egranata@google.com> wrote: > > > > > In many embedded systems, virtio-blk implementations are > > > backed by eMMC or UFS storage devices, which are subject to > > > predictable and measurable wear over time due to repeated write > > > cycles. > > > > > > For such systems, it can be important to be able to track > > > accurately the amount of wear imposed on the storage over > > > time and surface it to applications. In a native deployments > > > this is generally handled by the physical block device driver > > > but no such provision is made in virtio-blk to expose these > > > metrics for devices where it makes sense to do so. > > > > > > This patch adds support to virtio-blk for lifetime and wear > > > metrics to be exposed to the guest when a deployment of > > > virtio-blk is done over compatible eMMC or UFS storage. > > > > > > Signed-off-by: Enrico Granata <egranata@google.com> > > > --- > > > content.tex | 31 +++++++++++++++++++++++++++++-- > > > 1 file changed, 29 insertions(+), 2 deletions(-) > > > > > > diff --git a/content.tex b/content.tex > > > index 835f1ea..47e3566 100644 > > > --- a/content.tex > > > +++ b/content.tex > > > @@ -4418,6 +4418,9 @@ \subsection{Feature bits}\label{sec:Device Types > > > / Block Device / Feature bits} > > > > [something seems to have caused line wrapping in this patch] > > > > Hmm... I can try applying again and sending out as a v4? Please do, if we don't have any more changes on top. > > > > \item[VIRTIO_BLK_F_WRITE_ZEROES (14)] Device can support write zeroes command, > > > maximum write zeroes sectors size in \field{max_write_zeroes_sectors} and > > > maximum write zeroes segment number in \field{max_write_zeroes_seg}. > > > + > > > +\item[VIRTIO_BLK_F_LIFETIME (15)] Device supports providing storage lifetime > > > + information. > > > \end{description} > > > > > > \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types > > > / Block Device / Feature bits / Legacy Interface: Feature bits} > > > @@ -4601,14 +4604,16 @@ \subsection{Device Operation}\label{sec:Device > > > Types / Block Device / Device Ope > > > > > > The type of the request is either a read (VIRTIO_BLK_T_IN), a write > > > (VIRTIO_BLK_T_OUT), a discard (VIRTIO_BLK_T_DISCARD), a write zeroes > > > -(VIRTIO_BLK_T_WRITE_ZEROES), a flush (VIRTIO_BLK_T_FLUSH), or a get device ID > > > -string command (VIRTIO_BLK_T_GET_ID). > > > +(VIRTIO_BLK_T_WRITE_ZEROES), a flush (VIRTIO_BLK_T_FLUSH), a get device ID > > > +string command (VIRTIO_BLK_T_GET_ID), or a get device lifetime > > > +command (VIRTIO_BLK_T_GET_LIFETIME). > > > > > > \begin{lstlisting} > > > #define VIRTIO_BLK_T_IN 0 > > > #define VIRTIO_BLK_T_OUT 1 > > > #define VIRTIO_BLK_T_FLUSH 4 > > > #define VIRTIO_BLK_T_GET_ID 8 > > > +#define VIRTIO_BLK_T_GET_LIFETIME 10 > > > #define VIRTIO_BLK_T_DISCARD 11 > > > #define VIRTIO_BLK_T_WRITE_ZEROES 13 > > > \end{lstlisting} > > > @@ -4648,6 +4653,23 @@ \subsection{Device Operation}\label{sec:Device > > > Types / Block Device / Device Ope > > > \field{data}. The device ID string is a NUL-padded ASCII string up to 20 bytes > > > long. If the string is 20 bytes long then there is no NUL terminator. > > > > > > +The \field{data} used for VIRTIO_BLK_T_GET_LIFETIME requests is populated by > > > +the device, and is of the form: > > > + > > > +\begin{lstlisting} > > > +struct virtio_blk_lifetime { > > > + le16 pre_eol_info; > > > + le16 device_lifetime_est_a; > > > + le16 device_lifetime_est_b; > > > +}; > > > +\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 JEDEC > > > +standard No.84-B50 for the extended CSD register fields \field{PRE_EOL_INFO} > > > +\field{DEVICE_LIFETIME_EST_TYP_A} and \field{DEVICE_LIFETIME_EST_TYP_B} > > > +respectively. > > > > Do we have an explicit link to that JEDEC standard? > > > > I believe the specification is under a JEDEC paywall. I have access to > it by means of my employer, but it doesn't seem to be publicly > available. That's unfortunate... how much of the information in there is needed for someone to come up with a compliant implementation? Can we condense that to a sentence or two that would be unproblematic to put into the standard? If JEDEC is providing reasonable licensing terms, I guess it could also be an option to just refer to their homepage and specifying that standard (I think the full name is JESD84-B50 -- at least that's what my searching pointed to.) > > > > + > > > 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 > > > error or VIRTIO_BLK_S_UNSUPP for a request unsupported by device: > > > @@ -4754,6 +4776,11 @@ \subsection{Device Operation}\label{sec:Device > > > Types / Block Device / Device Ope > > > (case~\ref{item:flush3}). Failure to do so can cause data loss > > > in case of a crash. > > > > > > +If the device is backed by eMMC 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 as described in > > > this document > > > +cannot be obtained or have no useful meaning. > > > > Isn't that outside of the normative sections? If so, please make this a > > description without SHOULD and MUST NOT, and add them to the normative > > clauses. > > > > Hmm.. when I look at my local copy, I see this section right below the clause: > > "If the device is backed by persistent storage, the device MUST ensure that > stable writes are committed to it, before reporting completion of the write > (cases~\ref{item:flush1} and~\ref{item:flush2}) or the flush > (case~\ref{item:flush3}). Failure to do so can cause data loss > in case of a crash." > > It looked like the right place to add this kind of clause to me, but > if I am wrong and you would like to see it moved, please do let me > know. Ah, sorry, my mistake; I must have slipped in the document, your addition is fine. > Maybe I really do just need to apply the patch again on a clean-slate > repository, if what I see locally does not align? > > > Also, are eMMC/UFS just examples (i.e. may other types of persistent > > storage provide these metrics as well?) > > > > I can't say I know of other hardware that provides identical metrics, > but it could be possible and maybe could be done by software > adaptation for other storage systems? If we can get potentially get the same metrics from other hardware, that sentence should probably be reworded a bit. What about: "If the device is backed by storage providing life time metrics (such as eMMC or UFS persistent storage), the device SHOULD offer the VIRTIO_BLK_F_LIFETIME flag." ?
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