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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 <jwi@linux.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
pull/683/head
Julian Wiedmann 2019-04-26 09:37:41 +02:00 committed by Martin Schwidefsky
parent 5a19d67027
commit a698e13728
1 changed files with 9 additions and 2 deletions
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11
drivers/s390/cio/qdio_main.c
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@ -205,17 +205,22 @@ static inline int get_buf_states(struct qdio_q *q, unsigned int bufnr,
int auto_ack, int merge_pending) int auto_ack, int merge_pending)
{ {
unsigned char __state = 0; unsigned char __state = 0;
int i; int i = 1;
if (is_qebsm(q)) if (is_qebsm(q))
return qdio_do_eqbs(q, state, bufnr, count, auto_ack); return qdio_do_eqbs(q, state, bufnr, count, auto_ack);
/* get initial state: */ /* get initial state: */
__state = q->slsb.val[bufnr]; __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) if (merge_pending && __state == SLSB_P_OUTPUT_PENDING)
__state = SLSB_P_OUTPUT_EMPTY; __state = SLSB_P_OUTPUT_EMPTY;
for (i = 1; i < count; i++) { for (; i < count; i++) {
bufnr = next_buf(bufnr); bufnr = next_buf(bufnr);
/* merge PENDING into EMPTY: */ /* 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) if (q->slsb.val[bufnr] != __state)
break; break;
} }
out:
*state = __state; *state = __state;
return i; return i;
} }