Comment out Kirks io-request priority hack until we can do this in a

civilized way which doesn't cause grief.

The problem is that it is not generally safe to cast a "struct bio
*" to a "struct buf *".  Things like ccd, vinum, ata-raid and GEOM
constructs bio's which are not entrails of a struct buf.

Also, curthread may or may not have anything to do with the I/O request
at hand.

The correct solution can either be to tag struct bio's with a
priority derived from the requesting threads nice and have disksort
act on this field, this wouldn't address the "silly-seek syndrome"
where two equal processes bang the diskheads from one edge to the
other of the disk repeatedly.

Alternatively, and probably better: a sleep should be introduced
either at the time the I/O is requested or at the time it is completed
where we can be sure to sleep in the right thread.

The sleep also needs to be in constant timeunits, 1/hz can be practicaly
any sub-second size, at high HZ the current code practically doesn't
do anything.

1 files changed, 5 insertions, 0 deletions

diff --git a/sys/kern/subr_disklabel.c b/sys/kern/subr_disklabel.c
index 8a7b70e..176dafe 100644
--- a/sys/kern/subr_disklabel.c
+++ b/sys/kern/subr_disklabel.c
@@ -50,6 +50,7 @@
 #include <sys/syslog.h>
 #include <machine/atomic.h>
 
+#ifdef notquite
 /*
  * Mutex to use when delaying niced I/O bound processes in bioqdisksort().
  */
@@ -61,6 +62,7 @@ dksort_init(void)
 	mtx_init(&dksort_mtx, "dksort", NULL, MTX_DEF);
 }
 SYSINIT(dksort, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, dksort_init, NULL)
+#endif
 
 /*
  * Seek sort for disks.
@@ -85,6 +87,8 @@ bioqdisksort(bioq, bp)
 	struct bio *bq;
 	struct bio *bn;
 	struct bio *be;
+
+#ifdef notquite
 	struct thread *td = curthread;
 	
 	if (td && td->td_ksegrp->kg_nice > 0) {
@@ -98,6 +102,7 @@ bioqdisksort(bioq, bp)
 			    td->td_ksegrp->kg_nice);
 		}
 	}
+#endif
 	if (!atomic_cmpset_int(&bioq->busy, 0, 1))
 		panic("Recursing in bioqdisksort()");
 	be = TAILQ_LAST(&bioq->queue, bio_queue);