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scx_lavd: update cur_logical_clk atomically

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Previously, the cur_logical_clk is updated with WIRTE_ONCE(),
which does not guarantee the atomicity when concurrent writes happen
-- which is possible. So change it using CAS (compare-and-swap).

Signed-off-by: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Changwoo Min 2024-11-07 15:48:30 +09:00
parent b962ea8c35
commit e9ba2d53fa
1 changed files with 24 additions and 14 deletions
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38
scheds/rust/scx_lavd/src/bpf/main.bpf.c
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@ -458,26 +458,36 @@ static void update_stat_for_runnable(struct task_struct *p,
static void advance_cur_logical_clk(struct task_ctx *taskc)
{
struct sys_stat *stat_cur = get_sys_stat_cur();
u64 vlc, clc;
u64 vlc, clc, ret_clc;
u64 nr_queued, delta, new_clk;
/*
* The clock should not go backward, so do nothing.
*/
vlc = READ_ONCE(taskc->vdeadline_log_clk);
clc = READ_ONCE(cur_logical_clk);
if (vlc <= clc)
return;
/*
* Advance the clock up to the task's deadline. When overloaded,
* advance the clock slower so other can jump in the run queue.
*/
nr_queued = max(stat_cur->nr_queued_task, 1);
delta = (vlc - clc) / nr_queued;
new_clk = clc + delta;
for (int i = 0; i < LAVD_MAX_RETRY; ++i) {
/*
* The clock should not go backward, so do nothing.
*/
if (vlc <= clc)
return;
WRITE_ONCE(cur_logical_clk, new_clk);
/*
* Advance the clock up to the task's deadline. When overloaded,
* advance the clock slower so other can jump in the run queue.
*/
nr_queued = max(stat_cur->nr_queued_task, 1);
delta = (vlc - clc) / nr_queued;
new_clk = clc + delta;
ret_clc = __sync_val_compare_and_swap(&cur_logical_clk, clc, new_clk);
if (ret_clc == clc) /* CAS success */
return;
/*
* Retry with the updated clc
*/
clc = ret_clc;
}
}
static void update_stat_for_running(struct task_struct *p,