From a698e1372800b7e5dde2e461c1d3948c2e06032a Mon Sep 17 00:00:00 2001 From: Julian Wiedmann Date: Fri, 26 Apr 2019 09:37:41 +0200 Subject: s390/qdio: optimize state inspection of HW-owned SBALs When get_buf_states() gets called with count > 1, it scans the corresponding number of SBAL states until it encounters a mismatch. But when these SBALs are in a HW-owned state, the callers don't actually care _how many_ such SBALs are on the queue. If we can't process the first SBAL, we can't process any of the following SBALs either. So when the first SBAL is HW-owned, skip the scan of the remaining SBALs and thus save some CPU time. Signed-off-by: Julian Wiedmann Reviewed-by: Jens Remus Signed-off-by: Martin Schwidefsky --- drivers/s390/cio/qdio_main.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'drivers/s390/cio') diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c index be93172555ec..7b7620de2acd 100644 --- a/drivers/s390/cio/qdio_main.c +++ b/drivers/s390/cio/qdio_main.c @@ -205,17 +205,22 @@ static inline int get_buf_states(struct qdio_q *q, unsigned int bufnr, int auto_ack, int merge_pending) { unsigned char __state = 0; - int i; + int i = 1; if (is_qebsm(q)) return qdio_do_eqbs(q, state, bufnr, count, auto_ack); /* get initial state: */ __state = q->slsb.val[bufnr]; + + /* Bail out early if there is no work on the queue: */ + if (__state & SLSB_OWNER_CU) + goto out; + if (merge_pending && __state == SLSB_P_OUTPUT_PENDING) __state = SLSB_P_OUTPUT_EMPTY; - for (i = 1; i < count; i++) { + for (; i < count; i++) { bufnr = next_buf(bufnr); /* merge PENDING into EMPTY: */ @@ -228,6 +233,8 @@ static inline int get_buf_states(struct qdio_q *q, unsigned int bufnr, if (q->slsb.val[bufnr] != __state) break; } + +out: *state = __state; return i; } -- cgit v1.2.1