asim: fix io_overload

This test started failing after we fixed the skew distribution, since it relied
on the replica count on store 5 starting and ending at 0. After fixing the skew
distribution, the replica count on store 5 no longer began at 0, even though the
total leases/replica count on s5 didn’t change throughout the test which means
we weren't adding more leases/replicas to the s5. This change updates the test
to force the replica count on store 5 to start at 0 again.

Author: wenyihu6

pkg/kv/kvserver/asim/tests/testdata/non_rand/sma/io_overload.txt

@@ -1,11 +1,21 @@
+# This test verifies that the allocator correctly handles IO overload by
+# avoiding placement of replicas on stores that exceed the IO threshold. It
+# sets up a 5-node cluster where store 5 has an IO threshold of 1, causing it
+# to be considered overloaded and excluded from replica placement decisions.
+# It is expected that s5 will start with 0 replicas and stay at 0 replicas for
+# the duration of the test.
 skip_under_ci
 ----
 
 gen_cluster nodes=5
 ----
 
-gen_ranges ranges=500 placement_type=skewed
+gen_ranges ranges=500 placement_type=replica_placement
+{s1,s2,s3}:1
+{s1,s2,s4}:1
 ----
+{s1:*,s2,s3}:1
+{s1:*,s2,s4}:1
 
 set_capacity store=5 io_threshold=1
 ----
@@ -14,37 +24,21 @@ set_capacity store=5 io_threshold=1
 assertion type=stat stat=replicas stores=(5) exact_bound=0 ticks=5
 ----
 
-eval duration=10m seed=42 metrics=(replicas,leases) cfgs=(sma-count,mma-only)
+eval duration=5m seed=42 metrics=(replicas,leases) cfgs=(sma-count,mma-only)
 ----
-leases#1: first: [s1=259, s2=129, s3=64, s4=32, s5=16] (stddev=88.43, mean=100.00, sum=500)
-leases#1: last:  [s1=180, s2=102, s3=106, s4=106, s5=6] (stddev=55.34, mean=100.00, sum=500)
-leases#1: thrash_pct: [s1=23%, s2=23%, s3=20%, s4=27%, s5=0%]  (sum=93%)
-replicas#1: first: [s1=500, s2=456, s3=262, s4=165, s5=117] (stddev=153.29, mean=300.00, sum=1500)
-replicas#1: last:  [s1=347, s2=343, s3=348, s4=345, s5=117] (stddev=91.52, mean=300.00, sum=1500)
-replicas#1: thrash_pct: [s1=47%, s2=44%, s3=46%, s4=48%, s5=0%]  (sum=184%)
-artifacts[sma-count]: 937f126429994d65
-failed assertion sample 1
-  stat=replicas value=(=0.00) ticks=5
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
+leases#1: first: [s1=500, s2=0, s3=0, s4=0, s5=0] (stddev=200.00, mean=100.00, sum=500)
+leases#1: last:  [s1=329, s2=25, s3=75, s4=71, s5=0] (stddev=117.93, mean=100.00, sum=500)
+leases#1: thrash_pct: [s1=0%, s2=0%, s3=0%, s4=0%, s5=0%]  (sum=0%)
+replicas#1: first: [s1=500, s2=500, s3=250, s4=250, s5=0] (stddev=187.08, mean=300.00, sum=1500)
+replicas#1: last:  [s1=375, s2=375, s3=375, s4=375, s5=0] (stddev=150.00, mean=300.00, sum=1500)
+replicas#1: thrash_pct: [s1=0%, s2=0%, s3=3%, s4=0%, s5=0%]  (sum=3%)
+artifacts[sma-count]: 742eaa2acee55191
 ==========================
-leases#1: first: [s1=259, s2=129, s3=64, s4=32, s5=16] (stddev=88.43, mean=100.00, sum=500)
-leases#1: last:  [s1=259, s2=145, s3=64, s4=32, s5=0] (stddev=92.98, mean=100.00, sum=500)
+leases#1: first: [s1=500, s2=0, s3=0, s4=0, s5=0] (stddev=200.00, mean=100.00, sum=500)
+leases#1: last:  [s1=500, s2=0, s3=0, s4=0, s5=0] (stddev=200.00, mean=100.00, sum=500)
 leases#1: thrash_pct: [s1=0%, s2=0%, s3=0%, s4=0%, s5=0%]  (sum=0%)
-replicas#1: first: [s1=500, s2=456, s3=262, s4=165, s5=117] (stddev=153.29, mean=300.00, sum=1500)
-replicas#1: last:  [s1=500, s2=456, s3=262, s4=165, s5=117] (stddev=153.29, mean=300.00, sum=1500)
+replicas#1: first: [s1=500, s2=500, s3=250, s4=250, s5=0] (stddev=187.08, mean=300.00, sum=1500)
+replicas#1: last:  [s1=500, s2=500, s3=250, s4=250, s5=0] (stddev=187.08, mean=300.00, sum=1500)
 replicas#1: thrash_pct: [s1=0%, s2=0%, s3=0%, s4=0%, s5=0%]  (sum=0%)
-artifacts[mma-only]: 88981cebae8fb4b9
-failed assertion sample 1
-  stat=replicas value=(=0.00) ticks=5
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
-	store=5 stat=117.00
+artifacts[mma-only]: d6dfa8b63a078f25
 ==========================