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    Subject[patch 27/44] posix-cpu-timers: Provide array based access to expiry cache
    Using struct task_cputime for the expiry cache is a pretty odd choice and
    comes with magic defines to rename the fields for usage in the expiry
    cache.

    struct task_cputime is basically a u64 array with 3 members, but it has
    distinct members.

    The expiry cache content is different than the content of task_cputime
    because

    expiry[PROF] = task_cputime.stime + task_cputime.utime
    expiry[VIRT] = task_cputime.utime
    expiry[SCHED] = task_cputime.sum_exec_runtime

    So there is no direct mapping between task_cputime and the expiry cache and
    the #define based remapping is just a horrible hack.

    Having the expiry cache array based allows further simplification of the
    expiry code.

    To avoid an all in one cleanup which is hard to review add a temporary
    anonymous union into struct task_cputime which allows array based access to
    it. That requires to reorder the members. Add a build time sanity check to
    validate that the members are at the same place.

    The union and the build time checks will be removed after conversion.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    include/linux/posix-timers.h | 26 +++++++++++++++++++-------
    include/linux/sched/types.h | 4 ++--
    kernel/time/posix-cpu-timers.c | 10 ++++++++++
    3 files changed, 31 insertions(+), 9 deletions(-)

    --- a/include/linux/posix-timers.h
    +++ b/include/linux/posix-timers.h
    @@ -65,27 +65,39 @@ static inline int clockid_to_fd(const cl
    /*
    * Alternate field names for struct task_cputime when used on cache
    * expirations. Will go away soon.
    + *
    + * stime corresponds to CLOCKCPU_PROF
    + * utime corresponds to CLOCKCPU_VIRT
    + * sum_exex_runtime corresponds to CLOCKCPU_SCHED
    + *
    + * The ordering is currently enforced so struct task_cputime and the
    + * expiries array in struct posix_cputimers are equivalent.
    */
    -#define virt_exp utime
    #define prof_exp stime
    +#define virt_exp utime
    #define sched_exp sum_exec_runtime

    #ifdef CONFIG_POSIX_TIMERS
    /**
    * posix_cputimers - Container for posix CPU timer related data
    - * @cputime_expires: Earliest-expiration cache
    + * @cputime_expires: Earliest-expiration cache task_cputime based
    + * @expiries: Earliest-expiration cache array based
    * @cpu_timers: List heads to queue posix CPU timers
    *
    * Used in task_struct and signal_struct
    */
    struct posix_cputimers {
    - struct task_cputime cputime_expires;
    - struct list_head cpu_timers[CPUCLOCK_MAX];
    + /* Temporary union until all users are cleaned up */
    + union {
    + struct task_cputime cputime_expires;
    + u64 expiries[CPUCLOCK_MAX];
    + };
    + struct list_head cpu_timers[CPUCLOCK_MAX];
    };

    static inline void posix_cputimers_init(struct posix_cputimers *pct)
    {
    - memset(&pct->cputime_expires, 0, sizeof(pct->cputime_expires));
    + memset(&pct->expiries, 0, sizeof(pct->expiries));
    INIT_LIST_HEAD(&pct->cpu_timers[0]);
    INIT_LIST_HEAD(&pct->cpu_timers[1]);
    INIT_LIST_HEAD(&pct->cpu_timers[2]);
    @@ -96,13 +108,13 @@ static inline void posix_cputimers_group
    {
    posix_cputimers_init(pct);
    if (cpu_limit != RLIM_INFINITY)
    - pct->cputime_expires.prof_exp = cpu_limit * NSEC_PER_SEC;
    + pct->expiries[CPUCLOCK_PROF] = cpu_limit * NSEC_PER_SEC;
    }

    static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
    u64 runtime)
    {
    - pct->cputime_expires.sched_exp = runtime;
    + pct->expiries[CPUCLOCK_SCHED] = runtime;
    }

    /* Init task static initializer */
    --- a/include/linux/sched/types.h
    +++ b/include/linux/sched/types.h
    @@ -4,8 +4,8 @@

    /**
    * struct task_cputime - collected CPU time counts
    - * @utime: time spent in user mode, in nanoseconds
    * @stime: time spent in kernel mode, in nanoseconds
    + * @utime: time spent in user mode, in nanoseconds
    * @sum_exec_runtime: total time spent on the CPU, in nanoseconds
    *
    * This structure groups together three kinds of CPU time that are tracked for
    @@ -13,8 +13,8 @@
    * these counts together and treat all three of them in parallel.
    */
    struct task_cputime {
    - u64 utime;
    u64 stime;
    + u64 utime;
    unsigned long long sum_exec_runtime;
    };

    --- a/kernel/time/posix-cpu-timers.c
    +++ b/kernel/time/posix-cpu-timers.c
    @@ -18,6 +18,16 @@

    #include "posix-timers.h"

    +static inline void temporary_check(void)
    +{
    + BUILD_BUG_ON(offsetof(struct task_cputime, stime) !=
    + CPUCLOCK_PROF * sizeof(u64));
    + BUILD_BUG_ON(offsetof(struct task_cputime, utime) !=
    + CPUCLOCK_VIRT * sizeof(u64));
    + BUILD_BUG_ON(offsetof(struct task_cputime, sum_exec_runtime) !=
    + CPUCLOCK_SCHED * sizeof(u64));
    +}
    +
    static void posix_cpu_timer_rearm(struct k_itimer *timer);

    /*

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