From d6ac5fbd9cb6dd1931f31b607cec29a8deb4bf48 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Wed, 21 Aug 2024 13:13:59 -1000
Subject: [PATCH] scx_layered: Drop SCX_OPS_ENQ_LAST

The meaning of SCX_OPS_ENQ_LAST will change with future kernel updates and
enqueueing on local DSQ will no longer be sufficient to avoid stalls. No
reason to do it anyway. Just drop it.
---
 scheds/rust/scx_layered/src/bpf/intf.h     | 1 -
 scheds/rust/scx_layered/src/bpf/main.bpf.c | 7 -------
 scheds/rust/scx_layered/src/stats.rs       | 8 +-------
 3 files changed, 1 insertion(+), 15 deletions(-)

diff --git a/scheds/rust/scx_layered/src/bpf/intf.h b/scheds/rust/scx_layered/src/bpf/intf.h
index 59320d2..a58b16e 100644
--- a/scheds/rust/scx_layered/src/bpf/intf.h
+++ b/scheds/rust/scx_layered/src/bpf/intf.h
@@ -53,7 +53,6 @@ enum layer_stat_idx {
 	LSTAT_SEL_LOCAL,
 	LSTAT_ENQ_WAKEUP,
 	LSTAT_ENQ_EXPIRE,
-	LSTAT_ENQ_LAST,
 	LSTAT_ENQ_REENQ,
 	LSTAT_MIN_EXEC,
 	LSTAT_MIN_EXEC_NS,
diff --git a/scheds/rust/scx_layered/src/bpf/main.bpf.c b/scheds/rust/scx_layered/src/bpf/main.bpf.c
index 9fadfeb..2192d74 100644
--- a/scheds/rust/scx_layered/src/bpf/main.bpf.c
+++ b/scheds/rust/scx_layered/src/bpf/main.bpf.c
@@ -667,12 +667,6 @@ void BPF_STRUCT_OPS(layered_enqueue, struct task_struct *p, u64 enq_flags)
 	if (enq_flags & SCX_ENQ_REENQ) {
 		lstat_inc(LSTAT_ENQ_REENQ, layer, cctx);
 	} else {
-		if (enq_flags & SCX_ENQ_LAST) {
-			lstat_inc(LSTAT_ENQ_LAST, layer, cctx);
-			scx_bpf_dispatch(p, SCX_DSQ_LOCAL, slice_ns, 0);
-			return;
-		}
-
 		if (enq_flags & SCX_ENQ_WAKEUP)
 			lstat_inc(LSTAT_ENQ_WAKEUP, layer, cctx);
 		else
@@ -1698,5 +1692,4 @@ SCX_OPS_DEFINE(layered,
 	       .dump			= (void *)layered_dump,
 	       .init			= (void *)layered_init,
 	       .exit			= (void *)layered_exit,
-	       .flags			= SCX_OPS_ENQ_LAST,
 	       .name			= "layered");
diff --git a/scheds/rust/scx_layered/src/stats.rs b/scheds/rust/scx_layered/src/stats.rs
index 8cd88c1..e75f386 100644
--- a/scheds/rust/scx_layered/src/stats.rs
+++ b/scheds/rust/scx_layered/src/stats.rs
@@ -70,8 +70,6 @@ pub struct LayerStats {
     pub enq_wakeup: f64,
     #[stat(desc = "layer: % enqueued after slice expiration")]
     pub enq_expire: f64,
-    #[stat(desc = "layer: % enqueued as last runnable task on CPU")]
-    pub enq_last: f64,
     #[stat(desc = "layer: % re-enqueued due to RT preemption")]
     pub enq_reenq: f64,
     #[stat(desc = "layer: # times exec duration < min_exec_us")]
@@ -148,7 +146,6 @@ impl LayerStats {
         let ltotal = lstat(bpf_intf::layer_stat_idx_LSTAT_SEL_LOCAL)
             + lstat(bpf_intf::layer_stat_idx_LSTAT_ENQ_WAKEUP)
             + lstat(bpf_intf::layer_stat_idx_LSTAT_ENQ_EXPIRE)
-            + lstat(bpf_intf::layer_stat_idx_LSTAT_ENQ_LAST)
             + lstat(bpf_intf::layer_stat_idx_LSTAT_ENQ_REENQ);
         let lstat_pct = |sidx| {
             if ltotal != 0 {
@@ -181,7 +178,6 @@ impl LayerStats {
             sel_local: lstat_pct(bpf_intf::layer_stat_idx_LSTAT_SEL_LOCAL),
             enq_wakeup: lstat_pct(bpf_intf::layer_stat_idx_LSTAT_ENQ_WAKEUP),
             enq_expire: lstat_pct(bpf_intf::layer_stat_idx_LSTAT_ENQ_EXPIRE),
-            enq_last: lstat_pct(bpf_intf::layer_stat_idx_LSTAT_ENQ_LAST),
             enq_reenq: lstat_pct(bpf_intf::layer_stat_idx_LSTAT_ENQ_REENQ),
             min_exec: lstat_pct(bpf_intf::layer_stat_idx_LSTAT_MIN_EXEC),
             min_exec_us: (lstat(bpf_intf::layer_stat_idx_LSTAT_MIN_EXEC_NS) / 1000) as u64,
@@ -223,13 +219,12 @@ impl LayerStats {
 
         writeln!(
             w,
-            "  {:<width$}  tot={:7} local={} wake/exp/last/reenq={}/{}/{}/{}",
+            "  {:<width$}  tot={:7} local={} wake/exp/reenq={}/{}/{}",
             "",
             self.total,
             fmt_pct(self.sel_local),
             fmt_pct(self.enq_wakeup),
             fmt_pct(self.enq_expire),
-            fmt_pct(self.enq_last),
             fmt_pct(self.enq_reenq),
             width = header_width,
         )?;
@@ -350,7 +345,6 @@ impl SysStats {
         let total = lsum(bpf_intf::layer_stat_idx_LSTAT_SEL_LOCAL)
             + lsum(bpf_intf::layer_stat_idx_LSTAT_ENQ_WAKEUP)
             + lsum(bpf_intf::layer_stat_idx_LSTAT_ENQ_EXPIRE)
-            + lsum(bpf_intf::layer_stat_idx_LSTAT_ENQ_LAST)
             + lsum(bpf_intf::layer_stat_idx_LSTAT_ENQ_REENQ);
         let lsum_pct = |idx| {
             if total != 0 {