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authorJulian Wiedmann <jwi@linux.ibm.com>2020-05-08 17:00:21 +0200
committerVasily Gorbik <gor@linux.ibm.com>2020-06-16 13:44:03 +0200
commitc119a8a3c395b0850f131728bdddd166d172842f (patch)
treecb8ac6e24a24d0adc1cc99fe9f343a9ea909ea12 /drivers/s390
parentb3a9e3b9622ae10064826dccb4f7a52bd88c7407 (diff)
s390/qdio: fine-tune SLSB update
xchg() for a single-byte location assembles to a 4-byte Compare&Swap, wrapped into a non-trivial amount of retry code that deals with concurrent modifications to the unaffected bytes. Change it to a simple byte-store, but preserve the memory ordering semantics that the CS provided. This simplifies the generated code for a hot path, and in theory also allows us to amortize the memory barriers over multiple SLSB updates. CC: Andreas Krebbel <krebbel@linux.ibm.com> Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'drivers/s390')
-rw-r--r--drivers/s390/cio/qdio_main.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
index 610c05f59589..bb137f962c3f 100644
--- a/drivers/s390/cio/qdio_main.c
+++ b/drivers/s390/cio/qdio_main.c
@@ -254,10 +254,17 @@ static inline int set_buf_states(struct qdio_q *q, int bufnr,
if (is_qebsm(q))
return qdio_do_sqbs(q, state, bufnr, count);
+ /* Ensure that all preceding changes to the SBALs are visible: */
+ mb();
+
for (i = 0; i < count; i++) {
- xchg(&q->slsb.val[bufnr], state);
+ WRITE_ONCE(q->slsb.val[bufnr], state);
bufnr = next_buf(bufnr);
}
+
+ /* Make our SLSB changes visible: */
+ mb();
+
return count;
}