1. Feature Overview:
Feature Id: [74232]
a. Name of Feature: [6.3 FEAT] Enhanced DASD statistics for PAV and HPF - userspace part
b. Feature Description

This feature extends the DASD statistics feature to allow for a more detailed analysis of DASD I/O operations, especially in the context of zHPF and PAV:
??? The current ioctl statistics interface has no room for extensions and thus has to be replaced. This feature will create a debugfs based interface, which is flexible enough for future extensions.
??? The following data will be added to the statistics:
??? Time of last statistics reset.
??? Number of requests that were started on a PAV alias.
??? Number of requests that used High Performance FICON.
??? To be able to distinguish between read and write requests, a all relevant elements will be repeated in a version that counts read requests only.
??? The ioctl interface is limited to dasd block devices (dasda, dasdb, etc.). In the context of PAV or Hyper PAV however, requests that are started on one block device may be distributed by the device driver between several CCW devices (e.g. the base device 0.0.4711 and the alias device 0.0.4712). The ioctl interface does not allow to distinguish between PAV base and alias devices. The new debugfs interface allows to add statistics for each device.
??? The old proc, ioctl and tunedasd interfaces for reading statistics will be retained, but not extended. A new tool ???dasdstat??? will be used as user interface to the debugfs interface.
??? The new kernel interface allows to enable or disable statistics for individual entities. For example, it will be possible to enable only the global statistics, or only the statistics for dasda.

Upgrading from and coexisting with a previous version

To retain the semantic of the old statistics interface, one can still use /proc/dasd/statistics to enable or disable the global and block device statistics. The ioctl and tunedasd interfaces will allow to access the original subset of statistics data.
However, this will not prevent the users fromen- or disabling statistics via the new interface. For example:
If the global statistics and block statistics are enabled via the proc interface, then it is still possible to disable specific  statistics via the debugfs interface

2. Feature Details:
Sponsor: LTC zSeries BOE
Architectures:  zSeries - 64 native, 

Arch Specificity: purely arch specific code
Affects Kernel Modules: No
Delivery Mechanism: Backport
Category: other
Request Type: Package - Feature from IBM
d. Upstream Acceptance: In Progress
Sponsor Priority P1
f. Severity: high
IBM Confidential: No
Code Contribution: IBM code
g. Component Version Target: ---

3. Business Case
This feature enables improved diagnosis of PAV (Parallel Access Volume) and HPF (High Performance Ficon) environments to analyze and tune the DASD performance in a system, e.g. to give recommendations on the number of alias devices or the usage of Hyper PAV versus Base PAV.

4. Primary contact at Red Hat:
John Jarvis, jjarvis

5. Primary contacts at Partner:
Project Management Contact:
Hans-Georg Markgraf, mgrf.com

Technical contact(s):
Hans-Georg Markgraf, mgrf.com