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

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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.
This commit is contained in:
Poul-Henning Kamp 2002-04-22 06:53:20 +00:00
parent d435ac4e91
commit 29f88f470e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=95246
1 changed files with 5 additions and 0 deletions
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5
sys/kern/subr_disklabel.c
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@ -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);