[RFC PATCH 4/7] dyndbg: use static-key queueing API in dynamic-debug

[Jim Cromie <jim.cromie@gmail.com>]

Use the new static-key queueing API in dynamic-debug

function _get_cal_count() {
    # Sum all CPU columns for the 'CAL' (Function call interrupts) line
    grep CAL /proc/interrupts | awk '{ sum=0; for(i=2; i<NF-2; i++) sum+=$i; print sum }'
}
function ddcmdq () {
    local cal_before=$(_get_cal_count)
    echo $* > /proc/dynamic_debug/control
    local cal_after=$(_get_cal_count)
    printf "Delta-CAL (IPI): %d\n" "$((cal_after - cal_before))"
}

Before:

  #> ddcmdq +p
  #> ddcmdq -p
  ...
  [   37.165860] virtqueue callback for 000000009e760656 (00000000011de1b1)
  [   37.165952] virtiofs virtio0: virtio_fs_vq_done requests.0
  [   37.166119] dyndbg: query 0: "-p" mod:*
  Delta-CAL (IPI): 16154

After:
  ...
  [   32.189131] dyndbg: batch desc: ffffffff89468028, static_key addr ffffffff89468050 (fbcon_startup:1032)
  [   32.189225] dyndbg: batch desc: ffffffff89468060, static_key addr ffffffff89468088 (acpi_table_parse_entries_array:264)
  [   32.189332] dyndbg: batch desc: ffffffff89468098, static_key addr ffffffff894680c0 (acpi_table_print_madt_entry:229)
  Delta-CAL (IPI): 134

Extra context:

  #> wc /proc/dynamic_debug/control
  1903 15092 185427 /proc/dynamic_debug/control
  #> ddgrep dynamic_debug
  lib/dynamic_debug.c:386 [dynamic_debug]ddebug_change =_ "batch desc: %px, static_key addr %px (%s:%d)\n"
  lib/dynamic_debug.c:397 [dynamic_debug]ddebug_change =_ "applied queued updates to %d sites in total\n"
  #> dmesg | grep queued
  [   26.837520] dyndbg: applied queued updates to 1902 sites in total
  [   26.837631] applying 1866 queued jump_labels

The baseline has the 2 ratelimited patches cherry-picked in, so both
of these numbers include whatever overhead is caused by virtio and
dynamic-debugs pr_debug()s.

Cc: Jason Baron <jbaron@akamai.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index aa16782bc93b..e555a8dbdc27 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -371,10 +371,12 @@ static int ddebug_change(const struct ddebug_query *query, struct flag_settings
 #ifdef CONFIG_JUMP_LABEL
 			if (dp->flags & _DPRINTK_FLAGS_PRINT) {
 				if (!(newflags & _DPRINTK_FLAGS_PRINT))
-					static_branch_disable(&dp->key.dd_key_true);
+					static_branch_disable_queued(&dp->key.dd_key_true);
 			} else if (newflags & _DPRINTK_FLAGS_PRINT) {
-				static_branch_enable(&dp->key.dd_key_true);
+				static_branch_enable_queued(&dp->key.dd_key_true);
 			}
+			pr_debug("batch desc: %px, static_key addr %px (%s:%d)\n",
+				 dp, &dp->key.dd_key_true, dp->function, dp->lineno);
 #endif
 			v4pr_info("changed %s:%d [%s]%s %s => %s\n",
 				  trim_prefix(dp->filename), dp->lineno,
@@ -384,6 +386,8 @@ static int ddebug_change(const struct ddebug_query *query, struct flag_settings
 			dp->flags = newflags;
 		}
 	}
+	pr_debug("applied queued updates to %d sites in total\n", nfound);
+	static_key_apply_queued();
 	mutex_unlock(&ddebug_lock);
 
 	return nfound;
-- 
2.53.0