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| author | Julian Wiedmann <jwi@linux.ibm.com> | 2020-05-08 17:00:21 +0200 |
|---|---|---|
| committer | Vasily Gorbik <gor@linux.ibm.com> | 2020-06-16 13:44:03 +0200 |
| commit | c119a8a3c395b0850f131728bdddd166d172842f (patch) | |
| tree | cb8ac6e24a24d0adc1cc99fe9f343a9ea909ea12 /drivers/s390 | |
| parent | Linux 5.8-rc1 (diff) | |
| download | linux-c119a8a3c395b0850f131728bdddd166d172842f.tar.xz linux-c119a8a3c395b0850f131728bdddd166d172842f.zip | |
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.c | 9 |
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; } |