ipv6 lock contention with parallel socket io

[Adrian Chadd]

btw - just committed this to -HEAD.

I'll MFC it to stable/10 in a few days if noone raises any objections.

Thanks,


-a


On 31 December 2013 09:53, Adrian Chadd <adrian at freebsd.org> wrote:
> On 30 December 2013 23:35, Adrian Chadd <adrian at freebsd.org> wrote:
>> Hi,
>>
>> I've noticed a bunch of lock contention occurs when doing highly
>> parallel (> 4096 sockets) TCP IPv6 traffic.
>>
>> The contention is here:
>>
> [snip]
>
>>
>> .. it's the IF_ADATA lock surrounding the lla_lookup() calls.
>>
>> Now:
>>
>> * is there any reason this isn't an rmlock?
>> * the instance early on in nd6_output_lle() isn't taking the read
>> lock, it's taking the full lock. Is there any reason for this?
>>
>> I don't have much experience or time to spend on optimising the ipv6
>> code to scale better but this seems like one of those things that'll
>> bite us in the ass as the amount of ipv6 deployed increases.
>>
>> Does anyone have any ideas/suggestions on how we could improve things?
>
> This improves things quite a bit - from 1.9gbyte/sec @ 100% cpu usage
> to 2.7gbyte/sec @ 85% CPU usage. It's not perfect - the lock
> contention is still there - but it's much less of an issue now.
>
> Are there any issues with it?
>
> Index: sys/netinet6/nd6.c
> ===================================================================
> --- sys/netinet6/nd6.c  (revision 259475)
> +++ sys/netinet6/nd6.c  (working copy)
> @@ -1891,9 +1891,9 @@
>         flags = ((m != NULL) || (lle != NULL)) ? LLE_EXCLUSIVE : 0;
>         if (ln == NULL) {
>         retry:
> -               IF_AFDATA_LOCK(ifp);
> +               IF_AFDATA_RLOCK(ifp);
>                 ln = lla_lookup(LLTABLE6(ifp), flags, (struct sockaddr *)dst);
> -               IF_AFDATA_UNLOCK(ifp);
> +               IF_AFDATA_RUNLOCK(ifp);
>                 if ((ln == NULL) && nd6_is_addr_neighbor(dst, ifp))  {
>                         /*
>                          * Since nd6_is_addr_neighbor() internally
> calls nd6_lookup(),
>
>
> Thanks,
>
>
>
> -a