Commit b207f5a8 authored Nov 26, 2013 by Peter Oberparleiter Committed by Martin Schwidefsky Dec 16, 2013

s390/cio: Relax subchannel scan loop

The CIO layer scans for newly available I/O devices by performing a scan
of available subchannels using the Store Subchannel (STSCH) instruction.
This processing can take a significant amount of time during which no
other task can run on the same CPU (unless CONFIG_PREEMPT has been
enabled). As a result, scheduling latencies for other tasks are
increased noticeably, especially on a single-CPU system.

Fix this problem by explicitly allowing other tasks to be scheduled
each time a subchannel has been processed.

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Reviewed-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 449666dd

drivers/s390/cio/css.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -553,6 +553,9 @@ static int slow_eval_unknown_fn(struct subchannel_id schid, void *data)
		default:
		rc = 0;
		}
		/* Allow scheduling here since the containing loop might
		* take a while. */
		cond_resched();
		}
		return rc;
		}

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