Re: [PATCH] interconnect: Skip call into provider if initial bw is zero

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Hi Bryan,
Thanks for taking time to review the patch.

On 1/13/2023 5:40 PM, Bryan O'Donoghue wrote:
On 14/01/2023 01:24, Bryan O'Donoghue wrote:
On 13/01/2023 22:07, Vivek Aknurwar wrote:
Currently framework sets bw even when init bw requirements are zero during
provider registration, thus resulting bulk of set bw to hw.
Avoid this behaviour by skipping provider set bw calls if init bw is zero.

Signed-off-by: Vivek Aknurwar <quic_viveka@xxxxxxxxxxx>
---
  drivers/interconnect/core.c | 17 ++++++++++-------
  1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
index 25debde..43ed595 100644
--- a/drivers/interconnect/core.c
+++ b/drivers/interconnect/core.c
@@ -977,14 +977,17 @@ void icc_node_add(struct icc_node *node, struct icc_provider *provider)
      node->avg_bw = node->init_avg;
      node->peak_bw = node->init_peak;
-    if (provider->pre_aggregate)
-        provider->pre_aggregate(node);
-
-    if (provider->aggregate)
-        provider->aggregate(node, 0, node->init_avg, node->init_peak,
-                    &node->avg_bw, &node->peak_bw);
+    if (node->avg_bw || node->peak_bw) {
+        if (provider->pre_aggregate)
+            provider->pre_aggregate(node);
+
+        if (provider->aggregate)
+            provider->aggregate(node, 0, node->init_avg, node->init_peak,
+                        &node->avg_bw, &node->peak_bw);
+        if (provider->set)
+            provider->set(node, node);
+    }
-    provider->set(node, node);
      node->avg_bw = 0;
      node->peak_bw = 0;

I have the same comment/question for this patch that I had for the qcom arch specific version of it. This patch seems to be doing at a higher level what the patch below was doing at a lower level.

https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@xxxxxxxxxx/T/#m0c90588d0d1e2ab88c39be8f5f3a8f0b61396349

what happens to earlier silicon - qcom silicon which previously made explicit zero requests ?

This patch is to optimize and avoid all those bw 0 requests on each node addition during probe (which results in rpmh remote calls) for upcoming targets.


https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@xxxxxxxxxx/T/#m589e8280de470e038249bb362634221771d845dd

https://lkml.org/lkml/2023/1/3/1232

Isn't it a better idea to let lower layer drivers differentiate what they do ?

AFAIU lower layer driver can/should not differentiate between normal flow calls vs made as a result from probe/initialization of driver. Hence even bw 0 request is honored as like client in general wish to vote 0 as in an normal use case.


For example on pre 5.4 qcom kernel silicon we might choose to set the value to zero "because that's what the reference code did" but on newer silicon we might opt to skip the zero configuration ?

I'm happy to be shown the error of my ways but, absent testing to *show* it doesn't impact existing legacy silicon, I think we should be wary of this change.

---
bod

Oh, and what is the effect on Samsung and i.MX silicon interconnect providers of skipping the zero set ?

If interconnect providers are trying to clear bw votes coming from boot-loader then best place to clear those is in sync-state call back.


---
bod



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