Re: multipath: change the DEFAULT_MINIO for the request based multipath

["Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>]

Hi,

On 01/22/11 02:39, Malahal Naineni wrote:
> Christophe Varoqui [christophe.varoqui@gmail.com] wrote:
>>
>>> I'm not following why we'd need a different configuration parameter.
>>> It is just that the default rr_min_io that would be used would be
>>> conditional on the multipath target version being >= 1.1.0.
>>>
>> 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 [1] one top level default (hardcoded, superseded by config)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 [2] per hardware default (hardcoded, superseded by config)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).

>> Is my reasoning flawed ?
> 
> I don't think so. Your reasoning is right. How about this:
> 
> 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.
> 
> Note that devices can't have individual hardware default for request
> based mappings in this method and I think that should be OK. They are
> allowed to individual hardware based default for BIO based mappings as
> they have now. I will code it up if everyone agrees.

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.

Thanks,
-- 
Jun'ichi Nomura, NEC Corporation