s390/qdio: optimize state inspection of HW-owned SBALs (a698e137) · Commits · 戴 / test

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>

drivers/s390/cio/qdio_main.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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