Re: [PATCH v2] eventdev/timer: fix overflow issue

[Jerin Jacob <jerinjacobk@gmail.com>]

On Wed, Jan 25, 2023 at 2:16 AM Erik Gabriel Carrillo
<erik.g.carrillo@intel.com> wrote:
>
> The software timer adapter converts event timer timeout ticks to a
> number of CPU cycles at which an rte_timer should expire. The
> computation uses integer operations that can result in overflow.
>
> Use floating point operations instead to perform the computation, and
> convert the final result back to an integer type when returning. Also
> move the logic that checks the timeout range into the function that
> performs the above computation.
>
> Fixes: 6750b21bd6af ("eventdev: add default software timer adapter")
> Cc: stable@dpdk.org
>
> Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
> ---
> v2:
> * Fix implicit int to float conversion build warning on Clang

Not yet addressed the @Stephen Hemminger  comments on using of
rte_reciprocal. Also means to check what compute can be moved to
slowpath.
Marking as "Change requested", Looking for next version.


>
>  lib/eventdev/rte_event_timer_adapter.c | 71 ++++++++++++--------------
>  1 file changed, 34 insertions(+), 37 deletions(-)
>
> diff --git a/lib/eventdev/rte_event_timer_adapter.c b/lib/eventdev/rte_event_timer_adapter.c
> index d357f7403a..2efeb73bce 100644
> --- a/lib/eventdev/rte_event_timer_adapter.c
> +++ b/lib/eventdev/rte_event_timer_adapter.c
> @@ -719,13 +719,28 @@ swtim_callback(struct rte_timer *tim)
>         }
>  }
>
> -static __rte_always_inline uint64_t
> +static __rte_always_inline int
>  get_timeout_cycles(struct rte_event_timer *evtim,
> -                  const struct rte_event_timer_adapter *adapter)
> +                  const struct rte_event_timer_adapter *adapter,
> +                  uint64_t *timeout_cycles)
>  {
>         struct swtim *sw = swtim_pmd_priv(adapter);
> -       uint64_t timeout_ns = evtim->timeout_ticks * sw->timer_tick_ns;
> -       return timeout_ns * rte_get_timer_hz() / NSECPERSEC;
> +       uint64_t timeout_nsecs;
> +       double cycles_per_nsec;
> +
> +       cycles_per_nsec = (double)rte_get_timer_hz() / NSECPERSEC;
> +
> +       timeout_nsecs = evtim->timeout_ticks * sw->timer_tick_ns;
> +       if (timeout_nsecs > sw->max_tmo_ns)
> +               return -1;
> +       if (timeout_nsecs < sw->timer_tick_ns)
> +               return -2;
> +
> +       if (timeout_cycles)
> +               *timeout_cycles = (uint64_t)ceil(timeout_nsecs *
> +                                                cycles_per_nsec);
> +
> +       return 0;
>  }
>
>  /* This function returns true if one or more (adapter) ticks have occurred since
> @@ -759,23 +774,6 @@ swtim_did_tick(struct swtim *sw)
>         return false;
>  }
>
> -/* Check that event timer timeout value is in range */
> -static __rte_always_inline int
> -check_timeout(struct rte_event_timer *evtim,
> -             const struct rte_event_timer_adapter *adapter)
> -{
> -       uint64_t tmo_nsec;
> -       struct swtim *sw = swtim_pmd_priv(adapter);
> -
> -       tmo_nsec = evtim->timeout_ticks * sw->timer_tick_ns;
> -       if (tmo_nsec > sw->max_tmo_ns)
> -               return -1;
> -       if (tmo_nsec < sw->timer_tick_ns)
> -               return -2;
> -
> -       return 0;
> -}
> -
>  /* Check that event timer event queue sched type matches destination event queue
>   * sched type
>   */
> @@ -1195,21 +1193,6 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,
>                         break;
>                 }
>
> -               ret = check_timeout(evtims[i], adapter);
> -               if (unlikely(ret == -1)) {
> -                       __atomic_store_n(&evtims[i]->state,
> -                                       RTE_EVENT_TIMER_ERROR_TOOLATE,
> -                                       __ATOMIC_RELAXED);
> -                       rte_errno = EINVAL;
> -                       break;
> -               } else if (unlikely(ret == -2)) {
> -                       __atomic_store_n(&evtims[i]->state,
> -                                       RTE_EVENT_TIMER_ERROR_TOOEARLY,
> -                                       __ATOMIC_RELAXED);
> -                       rte_errno = EINVAL;
> -                       break;
> -               }
> -
>                 if (unlikely(check_destination_event_queue(evtims[i],
>                                                            adapter) < 0)) {
>                         __atomic_store_n(&evtims[i]->state,
> @@ -1225,7 +1208,21 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,
>                 evtims[i]->impl_opaque[0] = (uintptr_t)tim;
>                 evtims[i]->impl_opaque[1] = (uintptr_t)adapter;
>
> -               cycles = get_timeout_cycles(evtims[i], adapter);
> +               ret = get_timeout_cycles(evtims[i], adapter, &cycles);
> +               if (unlikely(ret == -1)) {
> +                       __atomic_store_n(&evtims[i]->state,
> +                                       RTE_EVENT_TIMER_ERROR_TOOLATE,
> +                                       __ATOMIC_RELAXED);
> +                       rte_errno = EINVAL;
> +                       break;
> +               } else if (unlikely(ret == -2)) {
> +                       __atomic_store_n(&evtims[i]->state,
> +                                       RTE_EVENT_TIMER_ERROR_TOOEARLY,
> +                                       __ATOMIC_RELAXED);
> +                       rte_errno = EINVAL;
> +                       break;
> +               }
> +
>                 ret = rte_timer_alt_reset(sw->timer_data_id, tim, cycles,
>                                           type, lcore_id, NULL, evtims[i]);
>                 if (ret < 0) {
> --
> 2.23.0
>