===============================================
QAT Acceleration for Encryption and Compression
===============================================

Intel QAT (QuickAssist Technology) can provide extended accelerated encryption
and compression services by offloading the actual encryption and compression
request(s) to the hardware QuickAssist accelerators, which are more efficient
in terms of cost and power than general purpose CPUs for those specific
compute-intensive workloads.

See `QAT Support for Compression`_ and `QAT based Encryption for RGW`_.


QAT in the Software Stack 
=========================

Application developers can access QuickAssist features through the QAT API.
The QAT API is the top-level API for QuickAssist technology, and enables easy
interfacing between the customer application and the QuickAssist acceleration
driver.

The QAT API accesses the QuickAssist driver, which in turn drives the
QuickAssist Accelerator hardware. The QuickAssist driver is responsible for
exposing the acceleration services to the application software.

A user can write directly to the QAT API, or the use of QAT can be done via
frameworks that have been enabled by others including Intel (for example, zlib*,
OpenSSL* libcrypto*, and the Linux* Kernel Crypto Framework).

QAT Environment Setup
=====================
1. QuickAssist Accelerator hardware is necessary to make use of accelerated
   encryption and compression services. And QAT driver in kernel space have to
   be loaded to drive the hardware.

The driver package can be downloaded from `Intel Quickassist Technology`_.

2. The implementation for QAT based encryption is directly base on QAT API which
   is included the driver package. But QAT support for compression depends on
   QATzip project, which is a user space library which builds on top of the QAT
   API. Currently, QATzip speeds up gzip compression and decompression at the
   time of writing.

See `QATzip`_.

Implementation
==============
1. QAT based Encryption for RGW 

`OpenSSL support for RGW encryption`_ has been merged into Ceph, and Intel also
provides one `QAT Engine`_ for OpenSSL. So, theoretically speaking, QAT based
encryption in Ceph can be directly supported through OpenSSl+QAT Engine.

But the QAT Engine for OpenSSL currently supports chained operations only, and
so Ceph will not be able to utilize QAT hardware feature for crypto operations
based on OpenSSL crypto plugin. As a result, one QAT plugin based on native
QAT API is added into crypto framework.

2. QAT Support for Compression

As mentioned above, QAT support for compression is based on QATzip library in
user space, which is designed to take full advantage of the performance provided
by QuickAssist Technology. Unlike QAT based encryption, QAT based compression
is supported through a tool class for QAT acceleration rather than a compressor
plugin. The common tool class can transparently accelerate the existing compression
types, but only zlib compressor can be supported at the time of writing. So
user is allowed to use it to speed up zlib compressor as long as the QAT
hardware is available and QAT is capable to handle it.

Configuration
=============
1. QAT based Encryption for RGW 

Edit the Ceph configuration file to make use of QAT based crypto plugin::

    plugin crypto accelerator = crypto_qat

2. QAT Support for Compression

One CMake option have to be used to trigger QAT based compression::

    -DWITH_QATZIP=ON

Edit the Ceph configuration file to enable QAT support for compression::

    qat compressor enabled=true


.. _QAT Support for Compression: https://github.com/ceph/ceph/pull/19714
.. _QAT based Encryption for RGW: https://github.com/ceph/ceph/pull/19386
.. _Intel Quickassist Technology: https://01.org/intel-quickassist-technology
.. _QATzip: https://github.com/intel/QATzip
.. _OpenSSL support for RGW encryption: https://github.com/ceph/ceph/pull/15168
.. _QAT Engine: https://github.com/intel/QAT_Engine
