diff options
| author | Kunhai Dai <daikunhai@didiglobal.com> | 2026-10-19 08:54:12 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2026-10-29 07:38:28 -0600 |
| commit | 0150554a3f38e1850d5964102eb89a720c5fe789 (patch) | |
| tree | 382bdf6f48b5a19c7486e7a4fce18e8b05f276be /include | |
| parent | c810ee88cdab27f443c32270dc7c0eaad2cca3f8 (diff) | |
blk-iocost: publish hweights as one atomic value
current_hweight() publishes the cache generation and both weights with
separate stores. Refreshers running on different CPUs can interleave
their stores and leave a new generation paired with weights from an older
calculation. The compiler can also reorder the generation store before
the weight stores, so a reader that sees the new generation can accept
stale weights.
A stale weight is not only a reporting artifact. It feeds the cost
calculation and the donation logic, where an inconsistent combination can
lead to a zero divisor in transfer_surpluses().
In addition, the slow path rereads iocg->hweight_active/inuse after
publishing them, so the value it returns can be the one written by another
refresher instead of the locally computed one.
Pack the generation and both weights into a single atomic64_t and publish
them with one atomic write. Readers take one atomic snapshot and return
the local values. Weights are in [1, WEIGHT_ONE]; storing each minus one
preserves the full range in 16 bits and leaves 32 bits for the generation.
The two weight fields remain as the donation workspace used under
ioc->lock. Tracepoints decode the packed cache without refreshing it and
iocost_monitor.py is updated accordingly.
Developed with assistance from Claude Code (Anthropic): the assistant
drafted the packed representation, the helpers and the tracepoint/monitor
changes, and ran the checks listed below. The author reviewed the result
and remains responsible for it.
Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Signed-off-by: Kunhai Dai <daikunhai@didiglobal.com>
Tested-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Tao Cui <cuitao@kylinos.cn>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://patch.msgid.link/20261019125412.3123895-3-daikunhai@didiglobal.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/trace/events/iocost.h | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/include/trace/events/iocost.h b/include/trace/events/iocost.h index e772b1bc60d6..eb711343ce4f 100644 --- a/include/trace/events/iocost.h +++ b/include/trace/events/iocost.h @@ -34,6 +34,9 @@ DECLARE_EVENT_CLASS(iocost_iocg_state, ), TP_fast_assign( + u32 hwa, hwi; + + iocg_hweight_cache(iocg, &hwa, &hwi); __assign_str(devname); __assign_str(cgroup); __entry->now = now->now; @@ -44,8 +47,8 @@ DECLARE_EVENT_CLASS(iocost_iocg_state, __entry->vtime = vtime; __entry->weight = iocg->weight; __entry->inuse = iocg->inuse; - __entry->hweight_active = iocg->hweight_active; - __entry->hweight_inuse = iocg->hweight_inuse; + __entry->hweight_active = hwa; + __entry->hweight_inuse = hwi; ), TP_printk("[%s:%s] now=%llu:%llu vrate=%llu " |