> > > @@ -1373,7 +1374,7 @@ int ib_peek_cq(struct ib_cq *cq, int wc_
> > > static inline int ib_req_notify_cq(struct ib_cq *cq,
> > > enum ib_cq_notify cq_notify)
> > > {
> > > - return cq->device->req_notify_cq(cq, cq_notify);
> > > + return cq->device->req_notify_cq(cq, cq_notify, NULL);
> > > }
> > >
> > > /**
> >
> > Can't say I like this adding overhead in data path operations (and note this
> > can't be optimized out). And kernel consumers work without passing it in,
> > so it
> > hurts kernel code even for Chelsio. Granted, the cost is small here, but
> > these
> > things do tend to add up.
> >
> > It seems all Chelsio needs is to pass in a consumer index - so, how about a
> > new
> > entry point? Something like void set_cq_udata(struct ib_cq *cq, struct
> > ib_udata *udata)?
> >
>
> Adding a new entry point would hurt chelsio's user mode performance if
> if then requires 2 kernel transitions to rearm the cq.
No, it won't need 2 transitions - just an extra function call,
so it won't hurt performance - it would improve performance.
ib_uverbs_req_notify_cq would call
ib_uverbs_req_notify_cq()
{
ib_set_cq_udata(cq, udata)
ib_req_notify_cq(cq, cmd.solicited_only ?
IB_CQ_SOLICITED : IB_CQ_NEXT_COMP);
}
This way kernel consumers don't incur any overhead,
and in userspace users extra function call is dwarfed
by system call overhead.
> Passing in user data is sort of SOP for these sorts of verbs.
I don't see other examples. Where we did pass extra user data
is in non-data pass verbs such as create QP.
This is most inner tight loop in many ULPs, so we should be very careful
about adding code there - these things do add up.
See recent IRQ API update in kernel.
> How much does passing one more param cost for kernel users?
Donnu. I just reviewed the code.
It really should be up to patch submitter to check the performance
effect of his patch, if there might be any.
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