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Add cam_iosched_set_latfcn to set a latency callback for high latency.

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It's often useful to have a callback when an I/O takes more than a
threshold amount of time. This adds the infrastructure for periph
devices to register one.

One use-case is as a debugging aide when you need a semi-realtime
indication of an I/O outlier so you can trigger bus capture gear for
vendor analysis.

Sponsored by: Netflix, Inc
This commit is contained in:
Warner Losh 2018-11-15 16:02:45 +00:00
parent 204a1a4d4c
commit e5436ab5af
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=340453
2 changed files with 35 additions and 3 deletions
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35
sys/cam/cam_iosched.c
View File

@ -294,6 +294,9 @@ struct cam_iosched_softc {
uint32_t this_frac; /* Fraction of a second (1024ths) for this tick */
sbintime_t last_time; /* Last time we ticked */
struct control_loop cl;
sbintime_t max_lat; /* when != 0, if iop latency > max_lat, call max_lat_fcn */
cam_iosched_latfcn_t latfcn;
void *latarg;
#endif
};
@ -1171,6 +1174,21 @@ void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
OID_AUTO, "load", CTLFLAG_RD,
&isc->load, 0,
"scaled load average / 100");
SYSCTL_ADD_U64(ctx, n,
OID_AUTO, "latency_trigger", CTLFLAG_RW,
&isc->max_lat, 0,
"Latency treshold to trigger callbacks");
#endif
}
void
cam_iosched_set_latfcn(struct cam_iosched_softc *isc,
cam_iosched_latfcn_t fnp, void *argp)
{
#ifdef CAM_IOSCHED_DYNAMIC
isc->latfcn = fnp;
isc->latarg = argp;
#endif
}
@ -1510,10 +1528,21 @@ cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp,
printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd);
}
if (!(bp->bio_flags & BIO_ERROR) && done_ccb != NULL)
cam_iosched_io_metric_update(isc,
cam_iosched_sbintime_t(done_ccb->ccb_h.qos.periph_data),
if (!(bp->bio_flags & BIO_ERROR) && done_ccb != NULL) {
sbintime_t sim_latency;
sim_latency = cam_iosched_sbintime_t(done_ccb->ccb_h.qos.periph_data);
cam_iosched_io_metric_update(isc, sim_latency,
bp->bio_cmd, bp->bio_bcount);
/*
* Debugging code: allow callbacks to the periph driver when latency max
* is exceeded. This can be useful for triggering external debugging actions.
*/
if (isc->latfcn && isc->max_lat != 0 && sim_latency > isc->max_lat)
isc->latfcn(isc->latarg, sim_latency, bp);
}
#endif
return retval;
}

3
sys/cam/cam_iosched.h
View File

@ -80,6 +80,8 @@ cam_iosched_sbintime_t(uintptr_t delta)
return (sbintime_t)((uint64_t)delta << CAM_IOSCHED_TIME_SHIFT);
}
typedef void (*cam_iosched_latfcn_t)(void *, sbintime_t, struct bio *);
int cam_iosched_init(struct cam_iosched_softc **, struct cam_periph *periph);
void cam_iosched_fini(struct cam_iosched_softc *);
void cam_iosched_sysctl_init(struct cam_iosched_softc *, struct sysctl_ctx_list *, struct sysctl_oid *);
@ -98,6 +100,7 @@ void cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags);
void cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags);
void cam_iosched_trim_done(struct cam_iosched_softc *isc);
int cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp, union ccb *done_ccb);
void cam_iosched_set_latfcn(struct cam_iosched_softc *isc, cam_iosched_latfcn_t, void *);
#endif
#endif