Messages in this thread Patch in this message | | | From | Eric Dumazet <> | Subject | [PATCH] account_system_vtime() should be a macro, not a function | Date | Thu, 19 Oct 2006 15:43:18 +0200 |
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[PATCH] account_system_vtime() should be a macro, not a function
Because the way 'current' is implemented on some archs, it's better to use a null macro for account_system_vtime(current)
I discovered that gcc was (correctly) issuing one useless instruction (to load %rax with current from pda) on x86_64 on irq_enter() and __irq_exit()
This saves few bytes in kernel size, on archs where current is 'asm volatile'
Sample of asm code :
<smp_apic_timer_interrupt>: ... callq <exit_idle> mov %gs:0x0,%rax // useless load of pda.'pcurrent' into %rax mov %gs:0x10,%rax addl $0x10000,0xffffffffffffe044(%rax) // add_preempt_count(HARDIRQ_OFFSET);
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> --- linux/include/linux/hardirq.h 2006-10-19 15:13:34.000000000 +0200 +++ linux-ed/include/linux/hardirq.h 2006-10-19 15:15:58.000000000 +0200 @@ -95,9 +95,11 @@ struct task_struct; #ifndef CONFIG_VIRT_CPU_ACCOUNTING -static inline void account_system_vtime(struct task_struct *tsk) -{ -} +/* + * It's better to provide a macro and not a function + * because the way 'current' is implemented on some archs + */ +#define account_system_vtime(X) do {} while (0) #endif /* | |