• Martin Schwidefsky's avatar
    [PATCH] idle cputime accounting · 79741dd3
    Martin Schwidefsky authored
    The cpu time spent by the idle process actually doing something is
    currently accounted as idle time. This is plain wrong, the architectures
    that support VIRT_CPU_ACCOUNTING=y can do better: distinguish between the
    time spent doing nothing and the time spent by idle doing work. The first
    is accounted with account_idle_time and the second with account_system_time.
    The architectures that use the account_xxx_time interface directly and not
    the account_xxx_ticks interface now need to do the check for the idle
    process in their arch code. In particular to improve the system vs true
    idle time accounting the arch code needs to measure the true idle time
    instead of just testing for the idle process.
    To improve the tick based accounting as well we would need an architecture
    primitive that can tell us if the pt_regs of the interrupted context
    points to the magic instruction that halts the cpu.
    
    In addition idle time is no more added to the stime of the idle process.
    This field now contains the system time of the idle process as it should
    be. On systems without VIRT_CPU_ACCOUNTING this will always be zero as
    every tick that occurs while idle is running will be accounted as idle
    time.
    
    This patch contains the necessary common code changes to be able to
    distinguish idle system time and true idle time. The architectures with
    support for VIRT_CPU_ACCOUNTING need some changes to exploit this.
    Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
    79741dd3
kernel_stat.h 2.12 KB