[ovs-dev] [urcu-fixes 1/4] timeval: Preserve quiescence across time_poll().

[Alex Wang]

This is a hard to notice one~,

Acked-by: Alex Wang <alexw at nicira.com>


On Mon, Apr 28, 2014 at 9:06 AM, Ben Pfaff <blp at nicira.com> wrote:

> Otherwise ovsrcu_synchronize() busy-waits in its loop because its
> poll_block() un-quiesces, causing the global_seqno to increase, which is
> what it waits for.
>
> Reported-by: Alex Wang <alexw at nicira.com>
> Signed-off-by: Ben Pfaff <blp at nicira.com>
> ---
>  lib/ovs-rcu.c |    7 +++++++
>  lib/ovs-rcu.h |    1 +
>  lib/timeval.c |   14 +++++++++-----
>  3 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/lib/ovs-rcu.c b/lib/ovs-rcu.c
> index 269f51b..b3c434d 100644
> --- a/lib/ovs-rcu.c
> +++ b/lib/ovs-rcu.c
> @@ -134,6 +134,13 @@ ovsrcu_quiesce(void)
>      ovsrcu_quiesced();
>  }
>
> +bool
> +ovsrcu_is_quiescent(void)
> +{
> +    ovsrcu_init();
> +    return pthread_getspecific(perthread_key) == NULL;
> +}
> +
>  static void
>  ovsrcu_synchronize(void)
>  {
> diff --git a/lib/ovs-rcu.h b/lib/ovs-rcu.h
> index 710870a..4b451b2 100644
> --- a/lib/ovs-rcu.h
> +++ b/lib/ovs-rcu.h
> @@ -178,5 +178,6 @@ void ovsrcu_postpone__(void (*function)(void *aux),
> void *aux);
>  void ovsrcu_quiesce_start(void);
>  void ovsrcu_quiesce_end(void);
>  void ovsrcu_quiesce(void);
> +bool ovsrcu_is_quiescent(void);
>
>  #endif /* ovs-rcu.h */
> diff --git a/lib/timeval.c b/lib/timeval.c
> index ebbdb98..d2a4380 100644
> --- a/lib/timeval.c
> +++ b/lib/timeval.c
> @@ -263,6 +263,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
> HANDLE *handles OVS_UNUSED,
>  {
>      long long int *last_wakeup = last_wakeup_get();
>      long long int start;
> +    bool quiescent;
>      int retval = 0;
>
>      time_init();
> @@ -274,6 +275,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
> HANDLE *handles OVS_UNUSED,
>      start = time_msec();
>
>      timeout_when = MIN(timeout_when, deadline);
> +    quiescent = ovsrcu_is_quiescent();
>
>      for (;;) {
>          long long int now = time_msec();
> @@ -287,10 +289,12 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
> HANDLE *handles OVS_UNUSED,
>              time_left = timeout_when - now;
>          }
>
> -        if (!time_left) {
> -            ovsrcu_quiesce();
> -        } else {
> -            ovsrcu_quiesce_start();
> +        if (!quiescent) {
> +            if (!time_left) {
> +                ovsrcu_quiesce();
> +            } else {
> +                ovsrcu_quiesce_start();
> +            }
>          }
>
>  #ifndef _WIN32
> @@ -313,7 +317,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
> HANDLE *handles OVS_UNUSED,
>          }
>  #endif
>
> -        if (time_left) {
> +        if (!quiescent && time_left) {
>              ovsrcu_quiesce_end();
>          }
>
> --
> 1.7.10.4
>
>
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