Commit 99269799 authored by Thomas Richter's avatar Thomas Richter Committed by Alexander Gordeev
Browse files

s390/pai: Fix missing PAI counter increments under heavy load 



Machines with a larger number of CPUs and under heavy load sometimes
loose PAI counter increments during recording using events
-e CRYPTO_ÂLL or -e NNPA_ALL. Counting is not affected.
This happens when several PAI crypto counters are incremented during
the same cryptographic operation.

During schedule out the functions

paiXXX_sched_task() (with XXX either crypt or ext)
+--> pai_have_samples()
   +--> pai_have_sample()
	+--> pai_copy()
	+--> pai_push_sample()

are called to read out PAI counter values.
In pai_copy() the current values of PAI counters are read from the
PMU memory mapped page and compared to the values read during last
schedule out operation, which have been saved in a backup page
named PAI_SAVE_AREA(event). For each PAI counter a delta is calculated
and when the delta is positive, that PAI counter was incremented by
hardware. This positve delta is reported as raw data record attached
to a sample.
After all deltas have been calculated, the new PAI counter values
are saved in the backup page PAI_SAVE_AREA(event). However this is
done in pai_push_sample(), leaving a small window for missing hardware
triggered updates. Here is one scenario:

  PAI counter idx:   0   1   2   3   4   5   6   7  ....  N
                   +---+---+---+---+---+---+---+---+    +---+
  PAI counter page:|   |   | X |   |   |   |   |   |....| Y |
                   +---+---+---+---+---+---+---+---+    +---+

In pai_copy() each PAI counter value is read and compared
to its old value. This is done in a loop. When PAI counter indexed
N is read, the hardware might increment PAI counter indexed 2 again,
updating its value from X to X+1.
Later pai_push_sample() simply mem-copies the complete PAI counter
page to a backup page and the increment of X+1 is lost, because the
backup page now contains the new value.

Read each PAI counter and save this value in the backup page when
there is a positive delta. This omits any time window between read
and store. This also reduced the work load as only modified PAI
counters are saved.

Cc: stable@vger.kernel.org
Fixes: fe861b0c ("s390/pai: save PAI counter value page in event structure")
Signed-off-by: default avatarThomas Richter <tmricht@linux.ibm.com>
Reviewed-by: default avatarSumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
parent 3fe7ecab

arch/s390/kernel/perf_pai.c

+20 −9
Original line number Diff line number Diff line
@@ -186,6 +186,13 @@ static u64 pai_getctr(unsigned long *page, int nr, unsigned long offset) 
	return page[nr];

}



static void pai_setctr(unsigned long *page, int nr, unsigned long offset, u64 v)

{

	if (offset)

		nr += offset / sizeof(*page);

	page[nr] = v;

}



/* Read the counter values. Return value from location in CMP. For base

 * event xxx_ALL sum up all events. Returns counter value.

 */
@@ -551,6 +558,8 @@ static void paicrypt_del(struct perf_event *event, int flags) 
/* Create raw data and save it in buffer. Calculate the delta for each

 * counter between this invocation and the last invocation.

 * Returns number of bytes copied.

 * After reading from PAI counter page, save the read value to the old

 * page to calculate PAI counter deltas.

 * Saves only entries with positive counter difference of the form

 * 2 bytes: Number of counter

 * 8 bytes: Value of counter
@@ -562,16 +571,22 @@ static size_t pai_copy(struct pai_userdata *userdata, unsigned long *page, 
	int i, outidx = 0;



	for (i = 1; i <= pp->num_avail; i++) {

		u64 val = 0, val_old = 0;

		u64 val = 0, val_old = 0, val_k = 0, val_old_k = 0;



		if (!exclude_kernel) {

			val += pai_getctr(page, i, pp->kernel_offset);

			val_old += pai_getctr(page_old, i, pp->kernel_offset);

			val_k = pai_getctr(page, i, pp->kernel_offset);

			val_old_k = pai_getctr(page_old, i, pp->kernel_offset);

			if (val_k != val_old_k)

				pai_setctr(page_old, i, pp->kernel_offset, val_k);

		}

		if (!exclude_user) {

			val += pai_getctr(page, i, 0);

			val_old += pai_getctr(page_old, i, 0);

			val = pai_getctr(page, i, 0);

			val_old = pai_getctr(page_old, i, 0);

			if (val != val_old)

				pai_setctr(page_old, i, 0, val);

		}

		val += val_k;

		val_old += val_old_k;

		if (val >= val_old)

			val -= val_old;

		else
@@ -602,8 +617,6 @@ static size_t pai_copy(struct pai_userdata *userdata, unsigned long *page, 
static int pai_push_sample(size_t rawsize, struct pai_map *cpump,

			   struct perf_event *event)

{

	int idx = PAI_PMU_IDX(event);

	struct pai_pmu *pp = &pai_pmu[idx];

	struct perf_sample_data data;

	struct perf_raw_record raw;

	struct pt_regs regs;
@@ -634,8 +647,6 @@ static int pai_push_sample(size_t rawsize, struct pai_map *cpump, 


	overflow = perf_event_overflow(event, &data, &regs);

	perf_event_update_userpage(event);

	/* Save crypto counter lowcore page after reading event data. */

	memcpy((void *)PAI_SAVE_AREA(event), cpump->area, pp->area_size);

	return overflow;

}