Commit 57ad0d4a authored by Thomas Richter's avatar Thomas Richter Committed by Vasily Gorbik
Browse files

s390/cpum_sf: Cap sampling rate to prevent lsctl exception 



commit fcc43a7e ("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: 39d4a501 ("s390/cpum_sf: Adjust sampling interval to avoid hitting sample limits")
Signed-off-by: default avatarThomas Richter <tmricht@linux.ibm.com>
Reviewed-by: default avatarSumanth Korikkar <sumanthk@linux.ibm.com>
Reviewed-by: default avatarHendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent 598bbefa

arch/s390/kernel/perf_cpum_sf.c

+5 −1
Original line number Diff line number Diff line
@@ -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,