blk-iocost: Fix error on iocost_ioc_vrate_adj

Systemtap 4.2 is unable to correctly interpret the "u32 (*missed_ppm)[2]"
argument of the iocost_ioc_vrate_adj trace entry defined in
include/trace/events/iocost.h leading to the following error:

  /tmp/stapAcz0G0/stap_c89c58b83cea1724e26395efa9ed4939_6321_aux_6.c:78:8:
  error: expected ‘;’, ‘,’ or ‘)’ before ‘*’ token
   , u32[]* __tracepoint_arg_missed_ppm

That argument type is indeed rather complex and hard to read. Looking
at block/blk-iocost.c. It is just a 2-entry u32 array. By simplifying
the argument to a simple "u32 *missed_ppm" and adjusting the trace
entry accordingly, the compilation error was gone.

Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index db35ee682294c138ec78a048a34bd80aeb860a7d..3ab0c1c704b68f0a9d5574d2a76ea252f3cc950d 100644 (file)
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1591,7 +1591,7 @@ skip_surplus_transfers:
                                      vrate_min, vrate_max);
                }
 
-               trace_iocost_ioc_vrate_adj(ioc, vrate, &missed_ppm, rq_wait_pct,
+               trace_iocost_ioc_vrate_adj(ioc, vrate, missed_ppm, rq_wait_pct,
                                           nr_lagging, nr_shortages,
                                           nr_surpluses);
 
@@ -1600,7 +1600,7 @@ skip_surplus_transfers:
                        ioc->period_us * vrate * INUSE_MARGIN_PCT, 100);
        } else if (ioc->busy_level != prev_busy_level || nr_lagging) {
                trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),
-                                          &missed_ppm, rq_wait_pct, nr_lagging,
+                                          missed_ppm, rq_wait_pct, nr_lagging,
                                           nr_shortages, nr_surpluses);
        }
 

diff --git a/include/trace/events/iocost.h b/include/trace/events/iocost.h
index 7ecaa65b7106eb67a4400d16fd86f5cc620d7a8c..c2f580fd371b11e117be68238c8530bd88a84d1f 100644 (file)
--- a/include/trace/events/iocost.h
+++ b/include/trace/events/iocost.h
@@ -130,7 +130,7 @@ DEFINE_EVENT(iocg_inuse_update, iocost_inuse_reset,
 
 TRACE_EVENT(iocost_ioc_vrate_adj,
 
-       TP_PROTO(struct ioc *ioc, u64 new_vrate, u32 (*missed_ppm)[2],
+       TP_PROTO(struct ioc *ioc, u64 new_vrate, u32 *missed_ppm,
                u32 rq_wait_pct, int nr_lagging, int nr_shortages,
                int nr_surpluses),
 
@@ -155,8 +155,8 @@ TRACE_EVENT(iocost_ioc_vrate_adj,
                __entry->old_vrate = atomic64_read(&ioc->vtime_rate);;
                __entry->new_vrate = new_vrate;
                __entry->busy_level = ioc->busy_level;
-               __entry->read_missed_ppm = (*missed_ppm)[READ];
-               __entry->write_missed_ppm = (*missed_ppm)[WRITE];
+               __entry->read_missed_ppm = missed_ppm[READ];
+               __entry->write_missed_ppm = missed_ppm[WRITE];
                __entry->rq_wait_pct = rq_wait_pct;
                __entry->nr_lagging = nr_lagging;
                __entry->nr_shortages = nr_shortages;