commitlog: Introduce and use comitlog sched group
Nowadays all commitlog code runs in whatever sched group it's kicked
from. Since IO prio classes are going to be inherited from the current
sched group the commitlog IO loops should be moved into commitlog sched
group, not inherit a "random" one.
There are currently two places that need correct context for IO -- the
.cycle() method and segments replenisher.
`$ perf-simple-query --write -c2` results
--- Before the patch ---
194898.36 tps ( 56.3 allocs/op, 12.7 tasks/op, 54307 insns/op, 0 errors)
199286.23 tps ( 56.2 allocs/op, 12.7 tasks/op, 54375 insns/op, 0 errors)
199815.84 tps ( 56.2 allocs/op, 12.7 tasks/op, 54377 insns/op, 0 errors)
198260.98 tps ( 56.3 allocs/op, 12.7 tasks/op, 54380 insns/op, 0 errors)
198572.86 tps ( 56.2 allocs/op, 12.7 tasks/op, 54371 insns/op, 0 errors)
median 198572.86 tps ( 56.2 allocs/op, 12.7 tasks/op, 54371 insns/op, 0 errors)
median absolute deviation: 713.36
maximum: 199815.84
minimum: 194898.36
--- After the patch ---
194751.80 tps ( 56.3 allocs/op, 12.7 tasks/op, 54331 insns/op, 0 errors)
199084.70 tps ( 56.2 allocs/op, 12.7 tasks/op, 54389 insns/op, 0 errors)
195551.47 tps ( 56.3 allocs/op, 12.7 tasks/op, 54385 insns/op, 0 errors)
197953.47 tps ( 56.3 allocs/op, 12.7 tasks/op, 54386 insns/op, 0 errors)
198710.00 tps ( 56.3 allocs/op, 12.7 tasks/op, 54387 insns/op, 0 errors)
median 197953.47 tps ( 56.3 allocs/op, 12.7 tasks/op, 54386 insns/op, 0 errors)
median absolute deviation: 1131.24
maximum: 199084.70
minimum: 194751.80
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closes #14005
5aea6938ae