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SubjectRe: [patch 1/3] net: serialize hrtimer callback in sched_cbq
Peter Zijlstra wrote:
> On Tue, 2009-07-14 at 09:42 -0700, Linus Torvalds wrote:
>> On Tue, 14 Jul 2009, Peter Zijlstra wrote:
>>> Linus really hated the softirq mode, which is what prompted me to change
>>> that.
>>>
>>> Now, it might be he only hated the particular interface and the
>>> resulting code, but I think to remember he simply thought the whole
>>> thing daft.
>> Yes. And I hated the bugs it had.
>>
>> Don't make something as core as timers any more complicated. Don't take
>> locks in timers and then complain about deadlocks. If your locking is
>> broken, don't make the core timers be idiotically broken.
>>
>> Because it was. The code was a total mess to follow, and had bugs.
>
> How would something like the below work for people?

Would be fine to me.

It reduces the duplicated code as well as private structs for hrtimers &
tasklets. And finally your suggestion preserves the proper separation of the
hrtimers and the tasklets that are used as underlying concepts.

Regards,
Oliver (who wrote net/can/bcm.c)


>
> ---
> include/linux/hrtimer.h | 22 ++++++++++++++++++++--
> kernel/hrtimer.c | 23 ++++++++++++++++++++++-
> 2 files changed, 42 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
> index 4759917..e7559fe 100644
> --- a/include/linux/hrtimer.h
> +++ b/include/linux/hrtimer.h
> @@ -22,6 +22,7 @@
> #include <linux/wait.h>
> #include <linux/percpu.h>
> #include <linux/timer.h>
> +#include <linux/interrupt.h>
>
>
> struct hrtimer_clock_base;
> @@ -91,7 +92,6 @@ enum hrtimer_restart {
> * @function: timer expiry callback function
> * @base: pointer to the timer base (per cpu and per clock)
> * @state: state information (See bit values above)
> - * @cb_entry: list head to enqueue an expired timer into the callback list
> * @start_site: timer statistics field to store the site where the timer
> * was started
> * @start_comm: timer statistics field to store the name of the process which
> @@ -108,7 +108,6 @@ struct hrtimer {
> enum hrtimer_restart (*function)(struct hrtimer *);
> struct hrtimer_clock_base *base;
> unsigned long state;
> - struct list_head cb_entry;
> #ifdef CONFIG_TIMER_STATS
> int start_pid;
> void *start_site;
> @@ -116,6 +115,12 @@ struct hrtimer {
> #endif
> };
>
> +struct hrtimer_softirq {
> + struct hrtimer timer;
> + struct tasklet_struct tasklet;
> + enum hrtimer_restart (*function)(struct hrtimer *);
> +};
> +
> /**
> * struct hrtimer_sleeper - simple sleeper structure
> * @timer: embedded timer structure
> @@ -335,6 +340,19 @@ static inline void hrtimer_init_on_stack(struct hrtimer *timer,
> static inline void destroy_hrtimer_on_stack(struct hrtimer *timer) { }
> #endif
>
> +enum hrtimer_restart __hrtimer_softirq_trampoline(struct hrtimer *timer);
> +void __hrtimer_tasklet_trampoline(unsigned long data);
> +
> +static inline void hrtimer_softirq_init(struct hrtimer_softirq *stimer,
> + enum hrtimer_restart (*func)(struct hrtimer *),
> + clockid_t which_clock, enum hrtimer_mode mode)
> +{
> + hrtimer_init(&stimer->timer, which_clock, mode);
> + stimer->timer.function = __hrtimer_softirq_trampoline;
> + tasklet_init(&stimer->tasklet, __hrtimer_tasklet_trampoline, stimer);
> + stimer->function = func;
> +}
> +
> /* Basic timer operations: */
> extern int hrtimer_start(struct hrtimer *timer, ktime_t tim,
> const enum hrtimer_mode mode);
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index ab5eb70..dae063c 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1098,7 +1098,6 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
> clock_id = CLOCK_MONOTONIC;
>
> timer->base = &cpu_base->clock_base[clock_id];
> - INIT_LIST_HEAD(&timer->cb_entry);
> hrtimer_init_timer_hres(timer);
>
> #ifdef CONFIG_TIMER_STATS
> @@ -1141,6 +1140,28 @@ int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
> }
> EXPORT_SYMBOL_GPL(hrtimer_get_res);
>
> +enum hrtimer_restart __hrtimer_softirq_trampoline(struct hrtimer *timer)
> +{
> + struct hrtimer_softirq *stimer =
> + container_of(timer, struct hrtimer_softirq, timer);
> +
> + tasklet_hi_schedule(&timer->tasklet);
> +
> + return HRTIMER_NORESTART;
> +}
> +EXPORT_SYMBOL_GPL(__hrtimer_softirq_trampoline);
> +
> +void __hrtimer_tasklet_trampoline(unsigned long data)
> +{
> + struct hrtimer_softirq *stimer = (void *)data;
> + enum hrtimer_restart restart;
> +
> + restart = stimer->function(&stimer->timer);
> + if (restart != HRTIMER_NORESTART)
> + hrtimer_restart(&stimer->timer);
> +}
> +EXPORT_SYMBOL_GPL(__hrtimer_tasklet_trampoline);
> +
> static void __run_hrtimer(struct hrtimer *timer)
> {
> struct hrtimer_clock_base *base = timer->base;
>
> --
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