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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-02 11:55:40 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-22 15:27:42 -0700 |
| commit | 3ad81779ad35cd2e2ab34ba3f47f6f485696a105 (patch) | |
| tree | 9199ed5472dce8ac9e36bfc029579fee6cfa64cb /scripts | |
| parent | 96a39bc434f94e213df43859fb8b01acda902634 (diff) | |
| download | linux-3ad81779ad35cd2e2ab34ba3f47f6f485696a105.tar.bz2 | |
scripts: Make checkpatch.pl warn on expedited RCU grace periods
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 <paulmck@linux.vnet.ibm.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Diffstat (limited to 'scripts')
| -rwxr-xr-x | scripts/checkpatch.pl | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl index 90e1edc8dd42..976e7117edfb 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 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", |