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@molgen.mpg.de]
Sent: Wednesday, April 21, 2021 6:36 AM
To: Salil Mehta <redacted>
Cc: linuxarm@openeuler.org; netdev@vger.kernel.org; Linuxarm
[off-list ref]; linux-kernel@vger.kernel.org; Jeff Kirsher
[off-list ref]; intel-wired-lan@lists.osuosl.org; David S.
Miller [off-list ref]; Jakub Kicinski [off-list ref]
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.

quoted

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:

quoted

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 :(

 

quoted

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.

quoted

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. 

 

quoted

Cc: intel-wired-lan@lists.osuosl.org
Cc: Jeff Kirsher <redacted>
Signed-off-by: Salil Mehta <redacted>
--
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

quoted

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)

quoted

  	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.

quoted

  		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)

quoted

  		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