Re: [PATCH for-next 10/13] RDMA/hns: Remove unnecessary kzalloc

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On Wed, Jul 31, 2019 at 05:16:38PM +0800, c00284828 wrote:
>
> 在 2019/7/31 15:49, Leon Romanovsky 写道:
> > On Wed, Jul 31, 2019 at 10:43:01AM +0800, oulijun wrote:
> > > 在 2019/7/30 21:40, Leon Romanovsky 写道:
> > > > On Tue, Jul 30, 2019 at 04:56:47PM +0800, Lijun Ou wrote:
> > > > > From: Lang Cheng <chenglang@xxxxxxxxxx>
> > > > >
> > > > > For hns_roce_v2_query_qp and hns_roce_v2_modify_qp,
> > > > > we can use stack memory to create qp context data.
> > > > > Make the code simpler.
> > > > >
> > > > > Signed-off-by: Lang Cheng <chenglang@xxxxxxxxxx>
> > > > > ---
> > > > >   drivers/infiniband/hw/hns/hns_roce_hw_v2.c | 64 +++++++++++++-----------------
> > > > >   1 file changed, 27 insertions(+), 37 deletions(-)
> > > > >
> > > > > diff --git a/drivers/infiniband/hw/hns/hns_roce_hw_v2.c b/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
> > > > > index 1186e34..07ddfae 100644
> > > > > --- a/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
> > > > > +++ b/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
> > > > > @@ -4288,22 +4288,19 @@ static int hns_roce_v2_modify_qp(struct ib_qp *ibqp,
> > > > >   {
> > > > >   	struct hns_roce_dev *hr_dev = to_hr_dev(ibqp->device);
> > > > >   	struct hns_roce_qp *hr_qp = to_hr_qp(ibqp);
> > > > > -	struct hns_roce_v2_qp_context *context;
> > > > > -	struct hns_roce_v2_qp_context *qpc_mask;
> > > > > +	struct hns_roce_v2_qp_context ctx[2];
> > > > > +	struct hns_roce_v2_qp_context *context = ctx;
> > > > > +	struct hns_roce_v2_qp_context *qpc_mask = ctx + 1;
> > > > >   	struct device *dev = hr_dev->dev;
> > > > >   	int ret;
> > > > >
> > > > > -	context = kcalloc(2, sizeof(*context), GFP_ATOMIC);
> > > > > -	if (!context)
> > > > > -		return -ENOMEM;
> > > > > -
> > > > > -	qpc_mask = context + 1;
> > > > >   	/*
> > > > >   	 * In v2 engine, software pass context and context mask to hardware
> > > > >   	 * when modifying qp. If software need modify some fields in context,
> > > > >   	 * we should set all bits of the relevant fields in context mask to
> > > > >   	 * 0 at the same time, else set them to 0x1.
> > > > >   	 */
> > > > > +	memset(context, 0, sizeof(*context));
> > > > "struct hns_roce_v2_qp_context ctx[2] = {};" will do the trick.
> > > >
> > > > Thanks
> > > >
> > > > .
> > > In this case, the mask is actually writen twice. if you do this, will it bring extra overhead when modify qp?
> > I don't understand first part of your sentence, and "no" to second part.
> >
> > Thanks
>
> +	struct hns_roce_v2_qp_context ctx[2];
> +	struct hns_roce_v2_qp_context *context = ctx;
> +	struct hns_roce_v2_qp_context *qpc_mask = ctx + 1;
> ...
> +	memset(context, 0, sizeof(*context));
>  	memset(qpc_mask, 0xff, sizeof(*qpc_mask));
>
> ctx[2] ={} does look more simple, just like another function in patch.
> But ctx[1] will be written 0 before being written to 0xff, is it faster than twice memset ?

Are you seriously talking about this micro optimization while you have mailbox
allocation in your modify_qp function?

Thanks

>
> > >
> > >
> > .
> >



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