From 11ae2e1dc58304a48816fc8ca4afa8f2ef9d1bdf Mon Sep 17 00:00:00 2001 From: Aboorva Devarajan Date: Fri, 4 Sep 2026 08:28:30 +0530 Subject: [PATCH] powerpc/entry: Fix double accounting of user time on interrupt entry Since the switch to generic entry, an interrupt from user mode accounts user time twice: once in arch_interrupt_enter_prepare() and again in arch_enter_from_user_mode(), which irqentry_enter() invokes for the same interrupt: arch_interrupt_enter_prepare() account_cpu_user_entry() /* first */ irqentry_enter() arch_enter_from_user_mode() account_cpu_user_entry() /* second */ The second call charges the same interval again, because account_cpu_user_entry() accumulates the time spent in user mode since the last return to user space. The two calls come from the GENERIC_ENTRY preparation series, where each step was a no-op on its own. Commit 09a9d3a8499d ("powerpc: introduce arch_enter_from_user_mode") added the hook with the user-time accounting in it, but nothing called it yet. Commit 893082ac769b ("powerpc: Prepare for IRQ entry exit") copied interrupt_enter_prepare() verbatim into entry-common.h as arch_interrupt_enter_prepare(); that copy was equally unused, as handlers still called interrupt_enter_prepare(). Commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") made both live. On the syscall side it did the full conversion: system_call_exception() now accounts once through the hook via syscall_enter_from_user_mode(), rather than calling account_cpu_user_entry() directly. On the interrupt side it switched the handler macros to arch_interrupt_enter_prepare() followed by irqentry_enter(), which also runs the hook, but the accounting in arch_interrupt_enter_prepare() was not removed to match. The double accounting starts with that commit. With CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y this roughly doubles the reported user time of any workload that takes interrupts. The other accounting modes compile account_cpu_user_entry() to an empty stub, so they are not affected. Remove the accounting from arch_interrupt_enter_prepare() and rely on arch_enter_from_user_mode(), which already runs for both syscalls and interrupts. The duplicate account_stolen_time() call is removed the same way. On a pseries LPAR a busy loop reports 6s user time in 3s elapsed (~210% CPU) before the fix, and 3s (~105% CPU) after it: $ python3 -c 'while True: pass' & $ sleep 3; ps -p $! -o etime,time,pcpu ELAPSED TIME %CPU Before 00:03 00:00:06 210 After 00:03 00:00:03 105 A 50% load reports ~70% usr / 30% idle before the fix, and ~49% usr / 51% idle after it: $ taskset -c 6 stress-ng --cpu 1 --cpu-load 50 & $ mpstat -P 6 1 CPU %usr %idle Before 6 69.74 30.26 After 6 48.51 50.50 Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") Reviewed-by: Mukesh Kumar Chaurasiya (IBM) Signed-off-by: Aboorva Devarajan Tested-by: Venkat Rao Bagalkote Reviewed-by: Amit Machhiwal Reviewed-by: Ritesh Harjani (IBM) Reviewed-by: Christophe Leroy (CS GROUP) Signed-off-by: Madhavan Srinivasan Link: https://patch.msgid.link/20260904025831.3439809-1-aboorvad@linux.ibm.com --- arch/powerpc/include/asm/entry-common.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h index 80b07750b531..8e91489fdf2b 100644 --- a/arch/powerpc/include/asm/entry-common.h +++ b/arch/powerpc/include/asm/entry-common.h @@ -222,8 +222,6 @@ static inline void arch_interrupt_enter_prepare(struct pt_regs *regs) if (user_mode(regs)) { kuap_lock(); - account_cpu_user_entry(); - account_stolen_time(); } else { kuap_save_and_lock(regs); /*