Re: [PATCH] ib_core: Enable and expose force_mr module parameter

[Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

> On May 15, 2017, at 10:57 AM, Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> 
> On Mon, May 15, 2017 at 10:52:44AM -0400, Chuck Lever wrote:
>> The fourth parameter of the module_param_named macro is a set of
>> file permissions. Passing 0 there means that module parameter is
>> not created and that adding "options ib_core force_mr=1" to a
>> modprobe.conf file has no effect.
>> 
>> The default setting of rdma_rw_force_mr continues to be 0, or false.
>> 
>> Fixes: a060b5629ab0 ("IB/core: generic RDMA READ/WRITE API")
>> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> 
> Chuck,
> 
> Do we really need this parameter?

Hi Leon-

Christoph and Sagi introduced this with the new rdma_rw API.
The default behavior is to avoid the use of FRWR, even for
devices that can support FRWR but also work without. FRWR is
used only for iWARP devices, which require it; but FRWR can
have a (slight) negative performance impact, which is why it
is not the default.

The purpose of this module parameter is to enable the use of
FRWR for devices that can go either way, as a way to test the
FRWR capability when using those devices.

I'm not sure we _need_ to have the module parameter. But I've
certainly used it while developing the NFSD conversion to use
the rdma_rw API, since I have no iWARP devices here.


>> ---
>> drivers/infiniband/core/rw.c |    2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/infiniband/core/rw.c b/drivers/infiniband/core/rw.c
>> index dbfd854..1cc8f07 100644
>> --- a/drivers/infiniband/core/rw.c
>> +++ b/drivers/infiniband/core/rw.c
>> @@ -23,7 +23,7 @@ enum {
>> };
>> 
>> static bool rdma_rw_force_mr;
>> -module_param_named(force_mr, rdma_rw_force_mr, bool, 0);
>> +module_param_named(force_mr, rdma_rw_force_mr, bool, 0644);
>> MODULE_PARM_DESC(force_mr, "Force usage of MRs for RDMA READ/WRITE operations");
>> 
>> /*
>> 
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--
Chuck Lever



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