Warner Losh <i...@freebsd.org> wrote: > Author: imp > Date: Thu Aug 24 22:11:10 2017 > New Revision: 322863 > URL: https://svnweb.freebsd.org/changeset/base/322863 > > Log: > Expand the latency tracking array from 1.024s to 8.192s to help track > extreme outliers from dodgy drives. Adjust comments to reflect this, > and make sure that the number of latency buckets match in the two > places where it matters.
It also matters for the sysctl description in cam_iosched_iop_stats_sysctl_init(). Would you mind increasing LAT_BUCKETS a bit more? I've recently set it to 17 in ElectroBSD as writes to my laptop's disk occasionally take a while under load: fk@t520 ~ $sudo /usr/src/share/dtrace/bio-request-latency [...] ada0 BIO_WRITE value ------------- Distribution ------------- count 16 | 0 32 | 1 64 | 34 128 |@ 582 256 |@@@@@@@@@@ 10608 512 |@@@@@ 5574 1024 |@@ 2454 2048 |@@@@ 3872 4096 |@@@@ 4043 8192 |@@@@ 4115 16384 |@@@@@ 4953 32768 |@@@ 3656 65536 |@@ 2252 131072 |@ 764 262144 | 331 524288 | 291 1048576 | 53 2097152 | 9 4194304 | 4 8388608 | 6 16777216 | 2 33554432 | 0 ada0 BIO_READ value ------------- Distribution ------------- count 16 | 0 32 | 1 64 | 126 128 |@ 1205 256 |@@@@@ 6359 512 |@@@ 3987 1024 |@@ 2044 2048 |@ 1384 4096 |@@ 2853 8192 |@@@@@ 6012 16384 |@@@@@@ 7254 32768 |@@@@@ 6524 65536 |@@@@ 4945 131072 |@@@ 3006 262144 |@ 1194 524288 |@ 620 1048576 | 162 2097152 | 0 Disk Bio Type Requests | Latency in us | iops Throughput | avg stddev max min | ada0 BIO_FLUSH 253 | 145927 162796 1253731 10293 | 0 0 k/s ada0 BIO_WRITE 43604 | 30345 261090 30069820 61 | 43 1994 k/s ada0 BIO_READ 47676 | 56039 128083 1691813 63 | 47 1260 k/s While proper tuning helps, the latency stats are also useful on systems where the iosched limiters haven't been enabled (yet). Fabian
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