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cam/iosched: Add a counter of I/Os that take too long

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Add kern.cam.DEV.UNIT.iosched.too_long (to count I/Os taking too long)
and kern.cam.DEV.UNIT.bad_latency (to set this threshold, defaults to
500ms). Each class of I/O (read, write, trim) has its own counters and
thresholds.

Sponsored by:		Netflix
Reviewed by:		jhb
Differential Revision:	https://reviews.freebsd.org/D46033
This commit is contained in:
Warner Losh 2024-07-19 20:52:40 -06:00
parent 47fb5d2b13
commit e82644e59e
1 changed files with 21 additions and 0 deletions
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21
sys/cam/cam_iosched.c
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@ -271,6 +271,9 @@ struct iop_stats {
sbintime_t emvar;
sbintime_t sd; /* Last computed sd */
uint64_t too_long; /* Number of I/Os greater than bad lat threshold */
sbintime_t bad_latency; /* Latency threshold */
uint32_t state_flags;
#define IOP_RATE_LIMITED 1u
@ -856,6 +859,7 @@ cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios)
ios->total = 0;
ios->ema = 0;
ios->emvar = 0;
ios->bad_latency = SBT_1S / 2; /* Default to 500ms */
ios->softc = isc;
cam_iosched_limiter_init(ios);
}
@ -1046,6 +1050,15 @@ cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stat
OID_AUTO, "errs", CTLFLAG_RD,
&ios->errs, 0,
"# of transactions completed with an error");
SYSCTL_ADD_U64(ctx, n,
OID_AUTO, "too_long", CTLFLAG_RD,
&ios->too_long, 0,
"# of transactions completed took too long");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "bad_latency",
CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE,
&ios->bad_latency, 0, cam_iosched_sbintime_sysctl, "A",
"Threshold for counting transactions that took too long (in us)");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "limiter",
@ -1916,6 +1929,14 @@ cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency)
sbintime_t y, deltasq, delta;
int i;
/*
* Simple threshold: count the number of events that excede the
* configured threshold.
*/
if (sim_latency > iop->bad_latency) {
iop->too_long++;
}
/*
* Keep counts for latency. We do it by power of two buckets.
* This helps us spot outlier behavior obscured by averages.