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Explain a bit of tricky code dealing with trims and how it prevents

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starvation. These side effects aren't obvious without extremely
careful study, and are important to do just so.
This commit is contained in:
Warner Losh 2015-01-13 00:20:35 +00:00
parent 378c532c1f
commit 0ac665747d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=277101
2 changed files with 20 additions and 0 deletions
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10
sys/cam/ata/ata_da.c
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@ -1790,6 +1790,16 @@ adadone(struct cam_periph *periph, union ccb *done_ccb)
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);

10
sys/cam/scsi/scsi_da.c
View File

@ -3018,6 +3018,16 @@ dadone(struct cam_periph *periph, union ccb *done_ccb)
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);