Author: imp
Date: Tue Jan 13 00:20:35 2015
New Revision: 277101
URL: https://svnweb.freebsd.org/changeset/base/277101
Log:
Explain a bit of tricky code dealing with trims and how it prevents
starvation. These side effects aren't obvious without extremely
careful study, and are important to do just so.
Modified:
head/sys/cam/ata/ata_da.c
head/sys/cam/scsi/scsi_da.c
Modified: head/sys/cam/ata/ata_da.c
==============================================================================
--- head/sys/cam/ata/ata_da.c Tue Jan 13 00:11:56 2015 (r277100)
+++ head/sys/cam/ata/ata_da.c Tue Jan 13 00:20:35 2015 (r277101)
@@ -1790,6 +1790,16 @@ adadone(struct cam_periph *periph, union
TAILQ_INIT(&queue);
TAILQ_CONCAT(&queue, &softc->trim_req.bps, bio_queue);
+ /*
+ * Normally, the xpt_release_ccb() above would make sure
+ * that when we have more work to do, that work would
+ * get kicked off. However, we specifically keep
+ * trim_running set to 0 before the call above to allow
+ * other I/O to progress when many BIO_DELETE requests
+ * are pushed down. We set trim_running to 0 and call
+ * daschedule again so that we don't stall if there are
+ * no other I/Os pending apart from BIO_DELETEs.
+ */
softc->trim_running = 0;
adaschedule(periph);
cam_periph_unlock(periph);
Modified: head/sys/cam/scsi/scsi_da.c
==============================================================================
--- head/sys/cam/scsi/scsi_da.c Tue Jan 13 00:11:56 2015 (r277100)
+++ head/sys/cam/scsi/scsi_da.c Tue Jan 13 00:20:35 2015 (r277101)
@@ -3018,6 +3018,16 @@ dadone(struct cam_periph *periph, union
TAILQ_INIT(&queue);
TAILQ_CONCAT(&queue, &softc->delete_run_queue.queue,
bio_queue);
softc->delete_run_queue.insert_point = NULL;
+ /*
+ * Normally, the xpt_release_ccb() above would make sure
+ * that when we have more work to do, that work would
+ * get kicked off. However, we specifically keep
+ * delete_running set to 0 before the call above to
+ * allow other I/O to progress when many BIO_DELETE
+ * requests are pushed down. We set delete_running to 0
+ * and call daschedule again so that we don't stall if
+ * there are no other I/Os pending apart from
BIO_DELETEs.
+ */
softc->delete_running = 0;
daschedule(periph);
cam_periph_unlock(periph);
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