Re: [PATCH v3 9/9] scsi: ufshpb: Make host mode parameters configurable

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Feb 18, 2021 at 03:19:32PM +0200, Avri Altman wrote:
> We can make use of this commit, to elaborate some more of the host
> control mode logic, explaining what role play each and every variable.
> 
> While at it, allow those parameters to be configurable.
> 
> Signed-off-by: Avri Altman <avri.altman@wdc.com>
> ---
>  Documentation/ABI/testing/sysfs-driver-ufs |  68 ++++++
>  drivers/scsi/ufs/ufshpb.c                  | 254 +++++++++++++++++++--
>  drivers/scsi/ufs/ufshpb.h                  |  18 ++
>  3 files changed, 326 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-driver-ufs b/Documentation/ABI/testing/sysfs-driver-ufs
> index 0017eaf89cbe..1d72201c4953 100644
> --- a/Documentation/ABI/testing/sysfs-driver-ufs
> +++ b/Documentation/ABI/testing/sysfs-driver-ufs
> @@ -1322,3 +1322,71 @@ Description:	This entry shows the maximum HPB data size for using single HPB
>  		===  ========
>  
>  		The file is read only.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/activation_thld
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	In host control mode, reads are the major source of activation
> +		trials.  once this threshold hs met, the region is added to the
> +		"to-be-activated" list.  Since we reset the read counter upon
> +		write, this include sending a rb command updating the region
> +		ppn as well.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/normalization_factor
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	In host control mode, We think of the regions as "buckets".
> +		Those buckets are being filled with reads, and emptied on write.
> +		We use entries_per_srgn - the amount of blocks in a subregion as
> +		our bucket size.  This applies because HPB1.0 only concern a
> +		single-block reads.  Once the bucket size is crossed, we trigger
> +		a normalization work - not only to avoid overflow, but mainly
> +		because we want to keep those counters normalized, as we are
> +		using those reads as a comparative score, to make various decisions.
> +		The normalization is dividing (shift right) the read counter by
> +		the normalization_factor. If during consecutive normalizations
> +		an active region has exhaust its reads - inactivate it.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/eviction_thld_enter
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	Region deactivation is often due to the fact that eviction took
> +		place: a region become active on the expense of another. This is
> +		happening when the max-active-regions limit has crossed.
> +		In host mode, eviction is considered an extreme measure. We
> +		want to verify that the entering region has enough reads, and
> +		the exiting region has much less reads.  eviction_thld_enter is
> +		the min reads that a region must have in order to be considered
> +		as a candidate to evict other region.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/eviction_thld_exit
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	same as above for the exiting region. A region is consider to
> +		be a candidate to be evicted, only if it has less reads than
> +		eviction_thld_exit.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/read_timeout_ms
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	In order not to hang on to “cold” regions, we shall inactivate
> +		a region that has no READ access for a predefined amount of
> +		time - read_timeout_ms. If read_timeout_ms has expired, and the
> +		region is dirty - it is less likely that we can make any use of
> +		HPB-READing it.  So we inactivate it.  Still, deactivation has
> +		its overhead, and we may still benefit from HPB-READing this
> +		region if it is clean - see read_timeout_expiries.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/read_timeout_expiries
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	if the region read timeout has expired, but the region is clean,
> +		just re-wind its timer for another spin.  Do that as long as it
> +		is clean and did not exhaust its read_timeout_expiries threshold.
> +
> +What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/timeout_polling_interval_ms
> +Date:		February 2021
> +Contact:	Avri Altman <avri.altman@wdc.com>
> +Description:	the frequency in which the delayed worker that checks the
> +		read_timeouts is awaken.
> +>>>>>>> ef6bf08e666d... scsi: ufshpb: Make host mode parameters configurable

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