From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
The synchronize_rcu_expedited() and synchronize_sched_expedited()
expedited-grace-period primitives induce OS jitter, which can degrade
real-time response. This commit therefore adds a checkpatch.pl warning
on any patch adding them.
Note that this patch does not warn on synchronize_srcu_expedited()
because it does not induce OS jitter, courtesy of its otherwise
much-maligned read-side memory barriers.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Andy Whitcroft <a...@canonical.com>
Cc: Joe Perches <j...@perches.com>
---
scripts/checkpatch.pl | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 90e1edc8dd42..0658a5f3029a 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5011,6 +5011,7 @@ sub process {
"memory barrier without comment\n" .
$herecurr);
}
}
+
# check for waitqueue_active without a comment.
if ($line =~ /\bwaitqueue_active\s*\(/) {
if (!ctx_has_comment($first_line, $linenr)) {
@@ -5018,6 +5019,24 @@ sub process {
"waitqueue_active without comment\n" .
$herecurr);
}
}
+
+# Check for expedited grace periods that interrupt non-idle non-nohz
+# online CPUs. These expedited can therefore degrade real-time response
+# if used carelessly, and should be avoided where not absolutely
+# needed. It is always OK to use synchronize_rcu_expedited() and
+# synchronize_sched_expedited() at boot time (before real-time applications
+# start) and in error situations where real-time response is compromised in
+# any case. Note that synchronize_srcu_expedited() does -not- interrupt
+# other CPUs, so don't warn on uses of synchronize_srcu_expedited().
+# Of course, nothing comes for free, and srcu_read_lock() and
+# srcu_read_unlock() do contain full memory barriers in payment for
+# synchronize_srcu_expedited() non-interruption properties.
+ if ($line =~
/\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
+ WARN("EXPEDITED_RCU_GRACE_PERIOD",
+ "expedited RCU grace periods should be avoided in
cases where they can degrade real-time response\n" . $herecurr);
+
+ }
+
# check of hardware specific defines
if ($line =~
m@^.\s*\#\s*if.*\b(__i386__|__powerpc64__|__sun__|__s390x__)\b@ && $realfile !~
m@include/asm-@) {
CHK("ARCH_DEFINES",
--
1.8.1.5
--
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