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 /tools | |
| 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 'tools')
| -rw-r--r-- | tools/cgroup/iocost_monitor.py | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/tools/cgroup/iocost_monitor.py b/tools/cgroup/iocost_monitor.py index bdd78ba271b0..8a4f844c98d4 100644 --- a/tools/cgroup/iocost_monitor.py +++ b/tools/cgroup/iocost_monitor.py @@ -149,8 +149,11 @@ class IocgStat: self.weight = iocg.weight.value_() / WEIGHT_ONE self.active = iocg.active.value_() / WEIGHT_ONE self.inuse = iocg.inuse.value_() / WEIGHT_ONE - self.hwa_pct = iocg.hweight_active.value_() * 100 / WEIGHT_ONE - self.hwi_pct = iocg.hweight_inuse.value_() * 100 / WEIGHT_ONE + hweight_cache = iocg.hweight_cache.counter.value_() + hwa = ((hweight_cache >> 16) & (WEIGHT_ONE - 1)) + 1 + hwi = (hweight_cache & (WEIGHT_ONE - 1)) + 1 + self.hwa_pct = hwa * 100 / WEIGHT_ONE + self.hwi_pct = hwi * 100 / WEIGHT_ONE self.address = iocg.value_() vdone = iocg.done_vtime.counter.value_() |