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Re: [dm-devel] multipath: change the DEFAULT_MINIO for the request based multipath



On mar., 2011-01-25 at 18:23 -0800, Malahal Naineni wrote:
> Jun'ichi Nomura [j-nomura ce jp nec com] wrote:
> > >> Defaults are layered. For current minio, we have :
> > >> [1] one top level default (hardcoded, superseded by config)
> > >> [2] per hardware default (hardcoded, superseded by config)
> > >> [3] per multipath value (none hardcoded, defined by config)
> > >>
> > >> You suggest multipath-tools to adapt only the top level minio default
> > >> depending on dm-rq availability [1], but what of the hwtable defaults
> > >> [2] ? Should we provide vendors with a way to describe a with-rq minio
> > >> default *and* a without-rq minio default (a new parameter in the hwentry
> > >> struct) ? If so, we should also provide a new config file keyword to
> > >> override this new hwentry parameter hardcoded value ... then the
> > >> reasoning cascades to the mpentry struct minio setting [3].
> > >>
> > >> Actually, [1] is hardly the common case : only unknown hardware resort
> > >> to these defaults.
> > 
> > Do we really need [2]?
> > 
> > Currently, there seem only 3 minio values in per-hardware default:
> >   - 1000 (DEFAULT_MINIO)
> >   - 128
> >   - 100
> > 
> > I think both 128 and 100 are based on that, in many systems/cases,
> > max request size (max_sectors) is 512KB and BIO submission
> > is done in page-size unit (4KB).
> > 
> > If there isn't strong reason for the current default (1000)
> > (and I think there isn't), it seems we can remove [2]
> > after changing the default to 128 (or 100).
> > 
> > > 1. Set DEFAULT_MINIO to -1
> > > 2. If bio based mapping and the value is -1, set it to 1000
> > >    (DEFAULT_BIO_MINIO)
> > > 3. If request based mapping, set it to DEFAULT_REQUEST_MINIO.
> > 
> > Does it mean users can't change rr_min_io value for request-based dm?
> > I suspect it is possible that someone wants to set non-default
> > value to minio for request-based dm.
> 
> Your reading is correct that my proposal doesn't allow it. If we get away
> with [2] above (hwatable.c based values), then we can have something
> like this:
> 
> 1. Remove it from hwentry structure or set it to -1
> 2. If rr_minio is specified in the conf file (either through default or
>    device section etc), use it.
> 3. If not specified in the config file, use DEFAULT_BIO_MINIO or
>    DEFAULT_REQUEST_MINIO based on the multipath module version.
> 
> In other words, every device out there uses DEFAULT_BIO_MINIO or
> DEFAULT_REQUEST_MINIO if not specified by the administrator.
> Admin can override it in /etc/multipath.conf file.
> 
> CON: No per device controller default  (aka hwtable entry value)
> 
I pushed an implementation of the fully capable solution.

The behaviour is unchanged with dm-multipath <= 1.1.0
For newer driver, if no additional config is added to multipath.conf the
minio will be set to 1.

If Mike S. tests prove this value is not always optimal, it can be tuned
per device in hwtable (hwe->minio_rq) and overridden in multipath.conf
device{} and multipath{} section.

This seemed to be the most consistent behaviour, to me. But feel free to
disagree.

Please test carefully as the patch is quite invasive. I built and tested
lightly with a NetApp iSCSI simulator. The session produced the
following output

Feb 01 00:18:51 | --------start up--------
Feb 01 00:18:51 | read /etc/multipath.conf
Feb 01 00:18:51 | activate request-based multipathing mode (driver >=
v1.1.0)
...
Feb 01 00:18:51 | 360a980006e424377536f576c6274694f: rr_weight = 1
(controller setting)
Feb 01 00:18:51 | 360a980006e424377536f576c6274694f: minio = 2 rq
(controller setting)
Feb 01 00:18:51 | 360a980006e424377536f576c6274694f: no_path_retry =
NONE (internal default)
Feb 01 00:18:51 | 360a980006e424377536f576c6274694f: pg_timeout = NONE
(internal default)
Feb 01 00:18:51 | 360a980006e424377536f576c6274694f: set ACT_CREATE (map
does not exist)
Feb 01 00:18:51 | 360a980006e424377536f576c6274694f: load table [0 30720
multipath 1 queue_if_no_path 0 1 1 round-robin 0 1 1 8:16 2]
...

Seems right.

As a side effect, the new devmapper.c:dm_drv_get_version() can be used
by further developments ... like Mike S. 'pg_num == 0' recent patch.

Regards,
-- 
Christophe Varoqui <christophe varoqui opensvc com>
OpenSVC


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