s390/cpum_sf: Cap sampling rate to prevent lsctl exception

commit fcc43a7e294f ("s390/configs: Set HZ=1000") changed the interrupt
frequency of the system. On machines with heavy load and many perf event
overflows, this might lead to an exception. Dmesg displays these entries:
  [112.242542] cpum_sf: Loading sampling controls failed: op 1 err -22
One line per CPU online.

The root cause is the CPU Measurement sampling facility overflow
adjustment. Whenever an overflow (too much samples per tick) occurs, the
sampling rate is adjusted and increased. This was done without observing
the maximum sampling rate limit. When the current sampling interval is
higher than the maximum sampling rate limit, the lsctl instruction raises
an exception. The error messages is the result of such an exception.
Observe the upper limit when the new sampling rate is recalculated.

Cc: stable@vger.kernel.org
Fixes: 39d4a501a9ef ("s390/cpum_sf: Adjust sampling interval to avoid hitting sample limits")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index c92c29de725e814abf48298400a98b03a8a9ea85..7bfeb5208177d2eb61a05e1959cb2dcfceb5eeae 100644 (file)
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -1168,6 +1168,7 @@ static void hw_collect_samples(struct perf_event *event, unsigned long *sdbt,
 static void hw_perf_event_update(struct perf_event *event, int flush_all)
 {
        unsigned long long event_overflow, sampl_overflow, num_sdb;
+       struct cpu_hw_sf *cpuhw = this_cpu_ptr(&cpu_hw_sf);
        struct hw_perf_event *hwc = &event->hw;
        union hws_trailer_header prev, new;
        struct hws_trailer_entry *te;
@@ -1247,8 +1248,11 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all)
         * are dropped.
         * Slightly increase the interval to avoid hitting this limit.
         */
-       if (event_overflow)
+       if (event_overflow) {
                SAMPL_RATE(hwc) += DIV_ROUND_UP(SAMPL_RATE(hwc), 10);
+               if (SAMPL_RATE(hwc) > cpuhw->qsi.max_sampl_rate)
+                       SAMPL_RATE(hwc) = cpuhw->qsi.max_sampl_rate;
+       }
 }
 
 static inline unsigned long aux_sdb_index(struct aux_buffer *aux,