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MIPS: SMP: Don't increment irq_count multiple times for call function IPIs

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The majority of SMP platforms handle their IPIs through do_IRQ()
which calls irq_{enter/exit}(). When a call function IPI is received,
smp_call_function_interrupt() is called which also calls
irq_{enter,exit}(), meaning irq_count is raised twice.

When tick broadcasting is used (which is implemented via a call
function IPI), this incorrectly causes all CPU idle time on the core
receiving broadcast ticks to be accounted as time spent servicing
IRQs, as account_process_tick() will account as such if irq_count is
greater than 1. This results in 100% CPU usage being reported on a
core which receives its ticks via broadcast.

This patch removes the SMP smp_call_function_interrupt() wrapper which
calls irq_{enter,exit}(). Platforms which handle their IPIs through
do_IRQ() now call generic_smp_call_function_interrupt() directly to
avoid incrementing irq_count a second time. Platforms which don't
(loongson, sgi-ip27, sibyte) call generic_smp_call_function_interrupt()
wrapped in irq_{enter,exit}().

Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10770/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Alex Smith
2015-07-24 16:57:49 +01:00
committed by Ralf Baechle
parent 55fdcb2d56
commit 4ace6139bf
14 changed files with 30 additions and 31 deletions
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2
arch/mips/include/asm/smp.h
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@@ -83,8 +83,6 @@ static inline void __cpu_die(unsigned int cpu)
extern void play_dead(void);
#endif
extern asmlinkage void smp_call_function_interrupt(void);
static inline void arch_send_call_function_single_ipi(int cpu)
{
extern struct plat_smp_ops *mp_ops; /* private */