runqlen/cpuunclaimed: Fix runnable_weight issue after Linux 5.7

runqlen / cpuunclaimed add check_runnable_weight_field() as workaround to
check runnable_weight presents in struct cfs_rq in kernel/sched/sched.h by
trying to access runnable_weight field of struct
sched_entity in include/linux/sched.h. Please check more details in PR iovisor#1510
and iovisor#2164.

Unfortunately, the runnable_weight field of struct cfs_rq is removed, but the
runnable_weight field of struct sched_entity is remained by following patchset
series from Linux version 5.7.0.

- https://yhbt.net/lore/all/[email protected]/
- https://yhbt.net/lore/all/[email protected]/

Please also check the source of Linux below.

- include/linux/sched.h
    - https://elixir.bootlin.com/linux/v5.7/source/include/linux/sched.h#L475
- kernel/sched/sched.h
    - https://elixir.bootlin.com/linux/v5.7/source/kernel/sched/sched.h#L502

This PR checks runnable_weight field exists by using kernel_struct_has_field()
if target system with BTF enabled, otherwise fallback to legacy on-the-fly
compiling check. In the meantime, add Linux version 5.7.0 check in
structure definition cfs_rq_partial to prevent issue if target system
w/o BTF enabled and Linux version > 5.7.

Please check more details in iovisor#4602.

Signed-off-by: Ism Hong <[email protected]>

tools/cpuunclaimed.py

@@ -185,9 +185,12 @@ def check_runnable_weight_field():
 
 // Declare enough of cfs_rq to find nr_running, since we can't #import the
 // header. This will need maintenance. It is from kernel/sched/sched.h:
+// The runnable_weight field is removed from Linux 5.7.0
 struct cfs_rq_partial {
  struct load_weight load;
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 7, 0)
  RUNNABLE_WEIGHT_FIELD
+#endif
  unsigned int nr_running, h_nr_running;
 };
 
@@ -216,7 +219,10 @@ def check_runnable_weight_field():
 }
 """
 
-if check_runnable_weight_field():
+# If target has BTF enabled, use BTF to check runnable_weight field exists in
+# cfs_rq first, otherwise fallback to use check_runnable_weight_field().
+if BPF.kernel_struct_has_field(b'cfs_rq', b'runnable_weight') == 1 \
+ or check_runnable_weight_field():
  bpf_text = bpf_text.replace('RUNNABLE_WEIGHT_FIELD', 'unsigned long runnable_weight;')
 else:
  bpf_text = bpf_text.replace('RUNNABLE_WEIGHT_FIELD', '')

tools/runqlen.py

@@ -90,7 +90,7 @@ def check_runnable_weight_field():
 
  # Get a temporary file name
  tmp_file = NamedTemporaryFile(delete=False)
- tmp_file.close();
+ tmp_file.close()
 
  # Duplicate and close stderr (fd = 2)
  old_stderr = dup(2)
@@ -122,9 +122,12 @@ def check_runnable_weight_field():
 
 // Declare enough of cfs_rq to find nr_running, since we can't #import the
 // header. This will need maintenance. It is from kernel/sched/sched.h:
+// The runnable_weight field is removed from Linux 5.7.0
 struct cfs_rq_partial {
  struct load_weight load;
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 7, 0)
  RUNNABLE_WEIGHT_FIELD
+#endif
  unsigned int nr_running, h_nr_running;
 };
 
@@ -172,7 +175,10 @@ def check_runnable_weight_field():
  'BPF_HISTOGRAM(dist, unsigned int);')
  bpf_text = bpf_text.replace('STORE', 'dist.atomic_increment(len);')
 
-if check_runnable_weight_field():
+# If target has BTF enabled, use BTF to check runnable_weight field exists in
+# cfs_rq first, otherwise fallback to use check_runnable_weight_field().
+if BPF.kernel_struct_has_field(b'cfs_rq', b'runnable_weight') == 1 \
+ or check_runnable_weight_field():
  bpf_text = bpf_text.replace('RUNNABLE_WEIGHT_FIELD', 'unsigned long runnable_weight;')
 else:
  bpf_text = bpf_text.replace('RUNNABLE_WEIGHT_FIELD', '')