Re: [PATCHv2 for-next 1/3] RDMA/rtrs-clt: Print more info when an error happens

[Leon Romanovsky <leon@kernel.org>]

On Tue, Apr 13, 2021 at 05:31:24AM +0000, Haakon Bugge wrote:
> 
> 
> > On 12 Apr 2021, at 19:34, Leon Romanovsky <leon@kernel.org> wrote:
> > 
> > On Mon, Apr 12, 2021 at 04:00:55PM +0200, Gioh Kim wrote:
> >> On Mon, Apr 12, 2021 at 2:54 PM Jinpu Wang <jinpu.wang@ionos.com> wrote:
> >>> 
> >>> On Mon, Apr 12, 2021 at 2:41 PM Leon Romanovsky <leon@kernel.org> wrote:
> >>>> 
> >>>> On Mon, Apr 12, 2021 at 02:22:51PM +0200, Jinpu Wang wrote:
> >>>>> On Tue, Apr 6, 2021 at 2:41 PM Leon Romanovsky <leon@kernel.org> wrote:
> >>>>>> 
> >>>>>> On Tue, Apr 06, 2021 at 02:36:37PM +0200, Gioh Kim wrote:
> >>>>>>> From: Gioh Kim <gi-oh.kim@cloud.ionos.com>
> >>>>>>> 
> >>>>>>> Client prints only error value and it is not enough for debugging.
> >>>>>>> 
> >>>>>>> 1. When client receives an error from server:
> >>>>>>> the client does not only print the error value but also
> >>>>>>> more information of server connection.
> >>>>>>> 
> >>>>>>> 2. When client failes to send IO:
> >>>>>>> the client gets an error from RDMA layer. It also
> >>>>>>> print more information of server connection.
> >>>>>>> 
> >>>>>>> Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
> >>>>>>> Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
> >>>>>>> ---
> >>>>>>> drivers/infiniband/ulp/rtrs/rtrs-clt.c | 33 ++++++++++++++++++++++----
> >>>>>>> 1 file changed, 29 insertions(+), 4 deletions(-)
> >>>>>>> 
> >>>>>>> diff --git a/drivers/infiniband/ulp/rtrs/rtrs-clt.c b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> >>>>>>> index 5062328ac577..a534b2b09e13 100644
> >>>>>>> --- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> >>>>>>> +++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> >>>>>>> @@ -437,6 +437,11 @@ static void complete_rdma_req(struct rtrs_clt_io_req *req, int errno,
> >>>>>>>      req->in_use = false;
> >>>>>>>      req->con = NULL;
> >>>>>>> 
> >>>>>>> +     if (unlikely(errno)) {
> >>>>>> 
> >>>>>> I'm sorry, but all your patches are full of these likely/unlikely cargo
> >>>>>> cult. Can you please provide supportive performance data or delete all
> >>>>>> likely/unlikely in all rtrs code?
> >>>>> 
> >>>>> Hi Leon,
> >>>>> 
> >>>>> All the likely/unlikely from the non-fast path was removed as you
> >>>>> suggested in the past.
> >>>>> This one is on IO path, my understanding is for the fast path, with
> >>>>> likely/unlikely macro,
> >>>>> the compiler will optimize the code for better branch prediction.
> >>>> 
> >>>> In theory yes, in practice. gcc 10 generated same assembly code when I
> >>>> placed likely() and replaced it with unlikely() later.
> >> 
> >> Even-thought gcc 10 generated the same assembly code,
> >> there is no guarantee for gcc 11 or gcc 12.
> >> 
> >> I am reviewing rtrs source file and have found some unnecessary likely/unlikely.
> >> But I think likely/unlikely are necessary for extreme cases.
> >> I will have a discussion with my colleagues and inform you of the result.
> > 
> > Please come with performance data.
> 
> I think the best way to gather performance data is not remove the likely/unlikely, but swap their definitions. Less coding and more pronounced difference - if any.

In theory, it will multiply by 2 gain/loss, which is nice to see if
likely/ulikely change something.

Thanks

> 
> 
> Thxs, Håkon
>