linux-kernel - RE: [Intel-wired-lan] [PATCH V2 net] ice: Re-organizes reqstd/avail {R, T}XQ check/code for efficiency+readability

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Date:   Wed, 21 Apr 2021 07:41:13 +0000
From:   Salil Mehta <salil.mehta@...wei.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
CC:     "linuxarm@...neuler.org" <linuxarm@...neuler.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: RE: [Intel-wired-lan] [PATCH V2 net] ice: Re-organizes reqstd/avail
 {R, T}XQ check/code for efficiency+readability

> From: Paul Menzel [mailto:pmenzel@...gen.mpg.de]
> Sent: Wednesday, April 21, 2021 6:36 AM
> To: Salil Mehta <salil.mehta@...wei.com>
> Cc: linuxarm@...neuler.org; netdev@...r.kernel.org; Linuxarm
> <linuxarm@...wei.com>; linux-kernel@...r.kernel.org; Jeff Kirsher
> <jeffrey.t.kirsher@...el.com>; intel-wired-lan@...ts.osuosl.org; David S.
> Miller <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>
> Subject: Re: [Intel-wired-lan] [PATCH V2 net] ice: Re-organizes reqstd/avail
> {R, T}XQ check/code for efficiency+readability
> 
> Dear Salil,
> 
> 
> Thank you very much for your patch.

Thanks for the review.

> In the git commit message summary, could you please use imperative mood [1]?

No issues. There is always a scope of improvement.


> > Re-organize reqstd/avail {R, T}XQ check/code for efficiency+readability
> 
> It’s a bit long though. Maybe:
> 
> Avoid unnecessary assignment with user specified {R,T}XQs

Umm..above conveys the wrong meaning as this is not what patch is doing. 

If you see the code, in the presence of the user specified {R,T}XQs it
avoids fetching available {R,T}XQ count. 

What about below?

"Avoid unnecessary avail_{r,t}xq assignments if user has specified Qs"


> Am 14.04.21 um 00:44 schrieb Salil Mehta:
> > If user has explicitly requested the number of {R,T}XQs, then it is
> > unnecessary to get the count of already available {R,T}XQs from the
> > PF avail_{r,t}xqs bitmap. This value will get overridden by user specified
> > value in any case.
> >
> > This patch does minor re-organization of the code for improving the flow
> > and readabiltiy. This scope of improvement was found during the review of
> 
> readabil*it*y


Thanks. Missed that earlier. My shaky fingers :(

 
> > the ICE driver code.
> >
> > FYI, I could not test this change due to unavailability of the hardware.
> > It would be helpful if somebody can test this patch and provide Tested-by
> > Tag. Many thanks!
> 
> This should go outside the commit message (below the --- for example).

Agreed.

> > Fixes: 87324e747fde ("ice: Implement ethtool ops for channels")
> 
> Did you check the behavior before is actually a bug? Or is it just for
> the detection heuristic for commits to be applied to the stable series?

Right, later was the idea. 

 
> > Cc: intel-wired-lan@...ts.osuosl.org
> > Cc: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> > Signed-off-by: Salil Mehta <salil.mehta@...wei.com>
> > --
> > Change V1->V2
> >   (*) Fixed the comments from Anthony Nguyen(Intel)
> >       Link: https://lkml.org/lkml/2021/4/12/1997
> > ---
> >   drivers/net/ethernet/intel/ice/ice_lib.c | 14 ++++++++------
> >   1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/ice/ice_lib.c
> b/drivers/net/ethernet/intel/ice/ice_lib.c
> > index d13c7fc8fb0a..d77133d6baa7 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_lib.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_lib.c
> > @@ -161,12 +161,13 @@ static void ice_vsi_set_num_qs(struct ice_vsi *vsi, u16
> vf_id)
> >
> >   	switch (vsi->type) {
> >   	case ICE_VSI_PF:
> > -		vsi->alloc_txq = min3(pf->num_lan_msix,
> > -				      ice_get_avail_txq_count(pf),
> > -				      (u16)num_online_cpus());
> >   		if (vsi->req_txq) {
> >   			vsi->alloc_txq = vsi->req_txq;
> >   			vsi->num_txq = vsi->req_txq;
> > +		} else {
> > +			vsi->alloc_txq = min3(pf->num_lan_msix,
> > +					      ice_get_avail_txq_count(pf),
> > +					      (u16)num_online_cpus());
> >   		}
> 
> I am curious, did you check the compiler actually creates different
> code, or did it notice the inefficiency by itself and optimized it already?

I have not looked into that detail but irrespective of what compiler generates
I would like to keep the code in a shape which is more efficient and more readable.

I do understand in certain cases we have to do tradeoff between efficiency
and readability but I do not see that here.


> >   		pf->num_lan_tx = vsi->alloc_txq;
> > @@ -175,12 +176,13 @@ static void ice_vsi_set_num_qs(struct ice_vsi *vsi, u16
> vf_id)
> >   		if (!test_bit(ICE_FLAG_RSS_ENA, pf->flags)) {
> >   			vsi->alloc_rxq = 1;
> >   		} else {
> > -			vsi->alloc_rxq = min3(pf->num_lan_msix,
> > -					      ice_get_avail_rxq_count(pf),
> > -					      (u16)num_online_cpus());
> >   			if (vsi->req_rxq) {
> >   				vsi->alloc_rxq = vsi->req_rxq;
> >   				vsi->num_rxq = vsi->req_rxq;
> > +			} else {
> > +				vsi->alloc_rxq = min3(pf->num_lan_msix,
> > +						      ice_get_avail_rxq_count(pf),
> > +						      (u16)num_online_cpus());
> >   			}
> >   		}
> >
> 
> 
> Kind regards,
> 
> Paul