2016-04-08 11:07 GMT+08:00 Subash Abhinov Kasiviswanathan
<subashab@xxxxxxxxxxxxxx>:
> ip[6]tables currently waits for 1 second for the xtables lock to
> be freed if the -w option is used. We have seen that the lock is
> held much less than that resulting in unnecessary delay when
> trying to acquire the lock. This problem is even severe in case
> of latency sensitive applications.
>
> Introduce an exponential delay starting from 10ms (experimentally
> determined) up to a second.
>
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@xxxxxxxxxxxxxx>
> ---
> iptables/xshared.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/iptables/xshared.c b/iptables/xshared.c
> index 81c2581..d90ac13 100644
> --- a/iptables/xshared.c
> +++ b/iptables/xshared.c
> @@ -247,6 +247,7 @@ void xs_init_match(struct xtables_match *match)
> bool xtables_lock(int wait)
> {
> int fd, waited = 0, i = 0;
> + useconds_t base_delay = 10000;
>
> fd = open(XT_LOCK_NAME, O_CREAT, 0600);
> if (fd < 0)
> @@ -257,10 +258,15 @@ bool xtables_lock(int wait)
> return true;
> else if (wait >= 0 && waited >= wait)
> return false;
> - if (++i % 2 == 0)
> + if ((++i % 2 == 0) && (base_delay >= 200000))
> fprintf(stderr, "Another app is currently holding the xtables lock; "
> "waiting (%ds) for it to exit...\n", waited);
> waited++;
> - sleep(1);
This break the "-w" option's semantic, i.e. if the user input
"iptables -w 1", and concurrency happen,
we will just only wait 10ms and return an error.
> + if (base_delay > 1000000) {
> + sleep(1);
> + } else {
> + usleep(base_delay);
> + base_delay *= 2;
> + }
> }
> }
> --
> 1.8.2.1
>
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