Re: [PATCH 3/7] IB/srpt: Change default behavior from using SRQ to not using SRQ

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Tue, Oct 10, 2017 at 10:34:19AM -0400, Doug Ledford wrote:
> On 10/10/2017 12:14 AM, Leon Romanovsky wrote:
> > On Mon, Oct 09, 2017 at 05:01:33PM +0000, Bart Van Assche wrote:
> >> On Mon, 2017-10-09 at 12:56 -0400, Doug Ledford wrote:
> >>> On Sun, 2017-10-08 at 13:03 +0300, Leon Romanovsky wrote:
> >>>> It is a little bit strange to ask from user to decide if his adapter
> >>>> supports SRQ or not.
> >>>>
> >>>> It should be automatically.
> >>>
> >>> I think Bart's intent is that the driver not use SRQ as the default
> >>> behavior even if the adapter supports it, so querying the adapter for
> >>> support and enabling it if it exists would not achieve his desired
> >>> result.  This would then be used to override that behavior.  Is that
> >>> correct Bart?
> >>
> >> Hello Leon and Doug,
> >>
> >> The changes realized by this patch are:
> >> - Instead of using SRQ as default, use non-SRQ mode as default.
> >> - If SRQ has been chosen as default, and if SRQ is not supported, fall back
> >>   to non-SRQ mode (see also the if (IS_ERR(sdev->srq)) ... code).
> >>
> >> Please let me know if you have any further questions about this patch.
> >
> > Yes, in case HCA supports SRQ, when do you set that module parameter?
>
> You set it in your /etc/modprobe.d/ib_srp.conf file or the equivalent in
> your OS.

Doug,
But my question was "when" and not "how". When should I set this
parameter to true?

>
> > In the commit message, you mentioned disadvantages of using SRQ is a
> > default and among them - locks contention, which can be changed in the
> > future. Won't it mean that users stuck with current default, because
> > change of default will "break" their scripts?
>
> No, it won't.  If you change the default, you don't remove the variable,
> you just change what its setting is.  Then existing modprobe.d files
> become redundant, but nothing breaks.  People that don't want the new
> setting add a new file to the modprobe.d directory to change the option.

Not accurate, now I won't set any parameter because I'm relying on the
fact that the default is without SRQ. Once the default will be changed,
it will break my assumption.

>
> > Setting visible to user default won't allow us to change SRP behavior in
> > the future.
>
> No it doesn't.
>
> > I wouldn't recommend to make such option accessible by users.
> >
> > Thanks
> >
> >>
> >> Bart.
>
>
> --
> Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>     GPG Key ID: B826A3330E572FDD
>     Key fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD
>




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