Re: [PATCH] RDMA/iw_cxgb4: disable delayed ack by default

[Potnuri Bharat Teja <bharat@chelsio.com>]

On Sunday, September 09/13/20, 2020 at 12:43:25 +0530, Leon Romanovsky wrote:
> On Fri, Sep 11, 2020 at 09:39:57PM +0530, Potnuri Bharat Teja wrote:
> > On Friday, September 09/11/20, 2020 at 18:41:52 +0530, Leon Romanovsky wrote:
> > > On Thu, Sep 10, 2020 at 07:14:50PM +0000, Potnuri Bharat Teja wrote:
> > > > >> Subject: [PATCH] RDMA/iw_cxgb4: disable delayed ack by default
> > > > >>
> > > > >> Receive side delayed ack mode is needed only for certain area networks/ connections. Therefore disable it by default.
> > > > >>
> > > > >> Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
> > > > >> ---
> > > > >>  drivers/infiniband/hw/cxgb4/cm.c | 4 ++--
> > > > >>  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >>
> > > > >> diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c
> > > > >> index 1f288c73ccfc..8769e7aa097f 100644
> > > > >> --- a/drivers/infiniband/hw/cxgb4/cm.c
> > > > >> +++ b/drivers/infiniband/hw/cxgb4/cm.c
> > > > >> @@ -77,9 +77,9 @@ static int enable_ecn;  module_param(enable_ecn, int, 0644);  MODULE_PARM_DESC(enable_ecn, "Enable ECN (default=0/disabled)");
> > > > >>
> > > > >> -static int dack_mode = 1;
> > > > >> +static int dack_mode;
> > > > >>  module_param(dack_mode, int, 0644);
> > > > >> -MODULE_PARM_DESC(dack_mode, "Delayed ack mode (default=1)");
> > > > >> +MODULE_PARM_DESC(dack_mode, "Delayed ack mode (default=0)");
> > > > >
> > > > >Are you sure that this doesn't break user scripts?
> > > > Yes, I am sure. This does not interfere with user/kernel RDMA functionalities.
> > >
> > > How is it possible?
> > > Before this change user that did "modprobe iw_cxgb4" had delayed mode
> > > enabled, after this he will need to issue "modprobe iw_cxgb4 dack_mode=1"
> > >
> > Sorry I didnt get it right earlier. Yes now if user wants delayed ack mode,
> > user can issue "modprobe iw_cxgb4 dack_mode=1" or change it dynamically via
> > /sys/module/<>/paramters.
> > Chelsio adapters for better performance in most cases needs delayed ack mode to
> > be disabled. This change somehow got missed upstream all this while.
> > In fewer explicit cases, user can enable delayed ack mode where it is needed.
> 
> So why doesn't rdma-core have dack_mode=0 in kernel-boot scripts?
> 
Do you mean why dont I simply change rdma-hw-modules.rules instead?
I could do that if this is a user mode only setting. But this is needed for kernel 
mode too where in some cases rdma-core may not be installed.

Thanks.