From c8ba971cf8567d49eb5f43ee90c4e50424331c18 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 May 2026 15:16:37 +0200 Subject: powerpc/time: Prepare to stop elapsing in dynticks-idle Currently the tick subsystem stores the idle cputime accounting in private fields, allowing cohabitation with architecture idle vtime accounting. The former is fetched on online CPUs, the latter on offline CPUs. For consolidation purpose, architecture vtime accounting will continue to account the cputime but will make a break when the idle tick is stopped. The dyntick cputime accounting will then be relayed by the tick subsystem so that the idle cputime is still seen advancing coherently even when the tick isn't there to flush the idle vtime. Prepare for that and introduce three new APIs which will be used in subsequent patches: - vtime_dynticks_start() is deemed to be called when idle enters in dyntick mode. The idle cputime that elapsed so far is accumulated. - vtime_dynticks_stop() is deemed to be called when idle exits from dyntick mode. The vtime entry clocks are fast-forward to current time so that idle accounting restarts elapsing from now. - vtime_reset() is deemed to be called from dynticks idle IRQ entry to fast-forward the clock to current time so that the IRQ time is still accounted by vtime while nohz cputime is paused. Also accumulated vtime won't be flushed from dyntick-idle ticks to avoid accounting twice the idle cputime, along with nohz accounting. Signed-off-by: Frederic Weisbecker Signed-off-by: Thomas Gleixner Tested-by: Shrikanth Hegde Reviewed-by: Shrikanth Hegde Link: https://patch.msgid.link/20260508131647.43868-6-frederic@kernel.org --- arch/powerpc/kernel/time.c | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) (limited to 'arch') diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index b4472288e0d4..3460d1a5a97c 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -376,6 +376,47 @@ void vtime_task_switch(struct task_struct *prev) acct->starttime = acct0->starttime; } } + +#ifdef CONFIG_NO_HZ_COMMON +/** + * vtime_reset - Fast forward vtime entry clocks + * + * Called from dynticks idle IRQ entry to fast-forward the clocks to current time + * so that the IRQ time is still accounted by vtime while nohz cputime is paused. + */ +void vtime_reset(void) +{ + struct cpu_accounting_data *acct = get_accounting(current); + + acct->starttime = mftb(); +#ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME + acct->startspurr = read_spurr(acct->starttime); +#endif +} + +/** + * vtime_dyntick_start - Inform vtime about entry to idle-dynticks + * + * Called when idle enters in dyntick mode. The idle cputime that elapsed so far + * is accumulated and the tick subsystem takes over the idle cputime accounting. + */ +void vtime_dyntick_start(void) +{ + vtime_account_idle(current); +} + +/** + * vtime_dyntick_stop - Inform vtime about exit from idle-dynticks + * + * Called when idle exits from dyntick mode. The vtime entry clocks are + * fast-forward to current time so that idle accounting restarts elapsing from + * now. + */ +void vtime_dyntick_stop(void) +{ + vtime_reset(); +} +#endif /* CONFIG_NO_HZ_COMMON */ #endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */ void __no_kcsan __delay(unsigned long loops) -- cgit v1.2.3