On 01/11/2017 05:07 AM, Damien Le Moal wrote:

Matias,

On 1/10/17 22:06, Matias Bjorling wrote:

quoted

On 01/10/2017 05:24 AM, Theodore Ts'o wrote:

quoted

This may be an area where if we can create the right framework, and
fund some research work, we might be able to get some researchers and
their graduate students interested in doing some work in figuring out
what sort of divisions of responsibilities and hints back and forth
between the storage device and host have the most benefit.

That is a good idea. There is a couple of papers at FAST with
Open-Channel SSDs this year.  They look into the interface and various
ways to reduce latency fluctuations.

One thing I've heard a couple of times is the feature to move the GC
read/write process into the firmware. Enabling the host to offload GC
data movement, while the keeping the host in control. Would this be
beneficial for SMR?

Host-aware SMR drives already have GC internally implemented (for cases
when the host does not write sequentially). Host-managed drives do not.
As for moving an application specific GC code into the device, well,
code injection in the storage device is not for tomorrow, and likely not
ever.

There are however other clever ways to reduce GC related host overhead
with basic commands. For SCSI, these may be WRITE SCATTERED, EXTENDED
COPY, and some others can greatly improve overhead over a simple
read+write loop. A better approach to GC offload may not be a "GC"
command, but something more generic for moving around LBAs internally
within the device. That is, if existing commands are not satisfactory.

Hi Damien,

You're right. I was thinking of something similar to scattered
read/write to move data from one place to another. There is no
sector-granularity mapping table maintained by the OCSSD, which leaves
the logic up to the host.

Let me know if you decide to kick of a standardized interface for code
injection. Such an interface is long overdue. ;)