• Frederic Weisbecker's avatar
    cputime: Generic on-demand virtual cputime accounting · abf917cd
    Frederic Weisbecker authored
    If we want to stop the tick further idle, we need to be
    able to account the cputime without using the tick.
    Virtual based cputime accounting solves that problem by
    hooking into kernel/user boundaries.
    However implementing CONFIG_VIRT_CPU_ACCOUNTING require
    low level hooks and involves more overhead. But we already
    have a generic context tracking subsystem that is required
    for RCU needs by archs which plan to shut down the tick
    outside idle.
    This patch implements a generic virtual based cputime
    accounting that relies on these generic kernel/user hooks.
    There are some upsides of doing this:
    - This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING
    if context tracking is already built (already necessary for RCU in full
    tickless mode).
    - We can rely on the generic context tracking subsystem to dynamically
    (de)activate the hooks, so that we can switch anytime between virtual
    and tick based accounting. This way we don't have the overhead
    of the virtual accounting when the tick is running periodically.
    And one downside:
    - There is probably more overhead than a native virtual based cputime
    accounting. But this relies on hooks that are already set anyway.
    Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Li Zhong <zhong@linux.vnet.ibm.com>
    Cc: Namhyung Kim <namhyung.kim@lge.com>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
lppaca.h 4.7 KB