[PATCH 6.12 223/242] s390/perf_cpum_sf: Convert to use try_cmpxchg128()

Greg Kroah-Hartman
2026-04-08T18:48:53Z

From: Heiko Carstens <hca@linux.ibm.com>

[ Upstream commit e449399ffd295a1202b74a258227193454ef333f ]

Convert cmpxchg128() usages to try_cmpxchg128() in order to generate
slightly better code.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Stable-dep-of: 57ad0d4a00f5 ("s390/cpum_sf: Cap sampling rate to prevent lsctl exception")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/s390/kernel/perf_cpum_sf.c | 24 +++++++++---------------
1 file changed, 9 insertions(+), 15 deletions(-)

--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -1188,8 +1188,8 @@ static void hw_collect_samples(struct pe
static void hw_perf_event_update(struct perf_event *event, int flush_all)
{
unsigned long long event_overflow, sampl_overflow, num_sdb;
- union hws_trailer_header old, prev, new;
struct hw_perf_event *hwc = &event->hw;
+ union hws_trailer_header prev, new;
struct hws_trailer_entry *te;
unsigned long *sdbt, sdb;
int done;
@@ -1233,13 +1233,11 @@ static void hw_perf_event_update(struct
/* Reset trailer (using compare-double-and-swap) */
prev.val = READ_ONCE_ALIGNED_128(te->header.val);
do {
- old.val = prev.val;
new.val = prev.val;
new.f = 0;
new.a = 1;
new.overflow = 0;
- prev.val = cmpxchg128(&te->header.val, old.val, new.val);
- } while (prev.val != old.val);
+ } while (!try_cmpxchg128(&te->header.val, &prev.val, new.val));

/* Advance to next sample-data-block */
sdbt++;
@@ -1405,16 +1403,15 @@ static int aux_output_begin(struct perf_
static bool aux_set_alert(struct aux_buffer *aux, unsigned long alert_index,
unsigned long long *overflow)
{
- union hws_trailer_header old, prev, new;
+ union hws_trailer_header prev, new;
struct hws_trailer_entry *te;

te = aux_sdb_trailer(aux, alert_index);
prev.val = READ_ONCE_ALIGNED_128(te->header.val);
do {
- old.val = prev.val;
new.val = prev.val;
- *overflow = old.overflow;
- if (old.f) {
+ *overflow = prev.overflow;
+ if (prev.f) {
/*
* SDB is already set by hardware.
* Abort and try to set somewhere
@@ -1424,8 +1421,7 @@ static bool aux_set_alert(struct aux_buf
}
new.a = 1;
new.overflow = 0;
- prev.val = cmpxchg128(&te->header.val, old.val, new.val);
- } while (prev.val != old.val);
+ } while (!try_cmpxchg128(&te->header.val, &prev.val, new.val));
return true;
}

@@ -1454,7 +1450,7 @@ static bool aux_set_alert(struct aux_buf
static bool aux_reset_buffer(struct aux_buffer *aux, unsigned long range,
unsigned long long *overflow)
{
- union hws_trailer_header old, prev, new;
+ union hws_trailer_header prev, new;
unsigned long i, range_scan, idx;
unsigned long long orig_overflow;
struct hws_trailer_entry *te;
@@ -1486,17 +1482,15 @@ static bool aux_reset_buffer(struct aux_
te = aux_sdb_trailer(aux, idx);
prev.val = READ_ONCE_ALIGNED_128(te->header.val);
do {
- old.val = prev.val;
new.val = prev.val;
- orig_overflow = old.overflow;
+ orig_overflow = prev.overflow;
new.f = 0;
new.overflow = 0;
if (idx == aux->alert_mark)
new.a = 1;
else
new.a = 0;
- prev.val = cmpxchg128(&te->header.val, old.val, new.val);
- } while (prev.val != old.val);
+ } while (!try_cmpxchg128(&te->header.val, &prev.val, new.val));
*overflow += orig_overflow;
}