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> > > One thing I'm not so sure about is using a FCFS queue for the "time
> > > sensitive" requests.  I think that the average latency for requests from
> > > that queue is probably significantly increased by using FCFS rather than
> > > the increasing-block-number sort, because we lose the benefit of
> > > readahead, which will be particularly severe if the queues are long.  The
> > > sort seems particularly likely to be beneficial given the rather large
> > > number of requests we take from the queues in a "burst" and the consequent
> > > likelihood that we'd get a lot of track cache hits.
> > 
> > then how do you think about the attached one?
> 
> Just at a first glance, why three queues?
> 
> Thor

i forgot to attach a header part..

three queues are for
	- time sensitive requests.
		e.g. sync read/write, requests from pagedaemon(?)
	- time non sensitive requests which should be served by
	  some period because they will likely become time sensitive
	  requests later.
		e.g. read ahead
	- time non sensitive requests.
		e.g. delayed writes

YAMAMOTO Takashi


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Index: buf.h
===================================================================
--- buf.h	(revision 455)
+++ buf.h	(working copy)
@@ -110,6 +110,7 @@ struct bufq_state {
 #define BUFQ_FCFS		0x0010	/* First-come first-serve */
 #define BUFQ_DISKSORT		0x0020	/* Min seek sort */
 #define BUFQ_READ_PRIO		0x0030	/* Min seek and read priority */
+#define BUFQ_PRIOCSCAN		0x0040	/* Per-priority CSCAN */
 
 #define BUFQ_SORT_MASK		0x000f
 #define BUFQ_METHOD_MASK	0x00f0
@@ -153,6 +154,7 @@ struct buf {
 	struct simplelock b_interlock;	/* Lock for b_flags changes */
 	volatile long	b_flags;	/* B_* flags. */
 	int	b_error;		/* Errno value. */
+	int	b_prio;			/* Hint for buffer queue discipline. */
 	long	b_bufsize;		/* Allocated buffer size. */
 	long	b_bcount;		/* Valid bytes in buffer. */
 	long	b_resid;		/* Remaining I/O. */
@@ -191,12 +193,15 @@ struct buf {
 	LIST_ENTRY(buf) b_vnbufs;	/* Buffer's associated vnode. */
 	TAILQ_ENTRY(buf) b_freelist;	/* Free list position if not active. */
 	daddr_t	b_lblkno;		/* Logical block number. */
+
+	int b_bufqpriv;			/* XXX */
 };
 
 #define	BUF_INIT(bp)							\
 do {									\
 	LIST_INIT(&(bp)->b_dep);					\
 	simple_lock_init(&(bp)->b_interlock);				\
+	BIO_SETPRIO((bp), BPRIO_DEFAULT);				\
 } while (/*CONSTCOND*/0)
 
 /*
@@ -265,6 +270,15 @@ do {									\
 
 #ifdef _KERNEL
 
+#define	BIO_GETPRIO(bp)		((bp)->b_prio)
+#define	BIO_SETPRIO(bp, prio)	(bp)->b_prio = (prio)
+#define	BIO_COPYPRIO(bp1, bp2)	BIO_SETPRIO(bp1, BIO_GETPRIO(bp2))
+
+#define	BPRIO_TIMECRITICAL	2
+#define	BPRIO_TIMELIMITED	1
+#define	BPRIO_TIMENONCRITICAL	0
+#define	BPRIO_DEFAULT		BPRIO_TIMELIMITED
+
 extern	struct bio_ops bioops;
 extern	u_int nbuf;		/* The number of buffer headers */
 extern	struct buf *buf;	/* The buffer headers. */

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