Detect a slow raidz child during reads

A single slow responding disk can affect the overall read
performance of a raidz group.  When a raidz child disk is
determined to be a persistent slow outlier, then have it
sit out during reads for a period of time. The raidz group
can use parity to reconstruct the data that was skipped.

Each time a slow disk is placed into a sit out period, its
`vdev_stat.vs_slow_ios count` is incremented and a zevent
class `ereport.fs.zfs.delay` is posted.

The length of the sit out period can be changed using the
`raid_read_sit_out_secs` module parameter.  Setting it to
zero disables slow outlier detection.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Contributions-by: Don Brady <don.brady@klarasystems.com>
Contributions-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #17227

lib/libspl/include/sys/time.h

@@ -97,6 +97,15 @@ gethrestime_sec(void)
 	return (tv.tv_sec);
 }
 
+static inline hrtime_t
+getlrtime(void)
+{
+	struct timeval tv;
+	(void) gettimeofday(&tv, NULL);
+	return ((((uint64_t)tv.tv_sec) * NANOSEC) +
+	    ((uint64_t)tv.tv_usec * NSEC_PER_USEC));
+}
+
 static inline hrtime_t
 gethrtime(void)
 {