[ovs-dev] [PATCH v4 1/1] ovs-thread: Fix thread id for threads not started with ovs_thread_create()

Ilya Maximets i.maximets at samsung.com
Mon Jun 4 13:46:17 UTC 2018


On 04.06.2018 11:07, Eelco Chaudron wrote:
> When ping-pong'in a live VM migration between two machines running
> OVS-DPDK every now and then the ping misses would increase
> dramatically. For example:
> 
> ===========Stream Rate: 3Mpps===========
> No Stream_Rate Downtime Totaltime Ping_Loss Moongen_Loss
>  0       3Mpps      128     13974       115      7168374
>  1       3Mpps      145     13620        17      1169770
>  2       3Mpps      140     14499       116      7141175
>  3       3Mpps      142     13358        16      1150606
>  4       3Mpps      136     14004        16      1124020
>  5       3Mpps      139     15494       214     13170452
>  6       3Mpps      136     15610       217     13282413
>  7       3Mpps      146     13194        17      1167512
>  8       3Mpps      148     12871        16      1162655
>  9       3Mpps      137     15615       214     13170656
> 
> I identified this issue being introduced in OVS commit,
> f3e7ec254738 ("Update relevant artifacts to add support for DPDK 17.05.1.")
> and more specific due to DPDK commit,
> af1475918124 ("vhost: introduce API to start a specific driver").
> 
> The combined changes no longer have OVS start the vhost socket polling
> thread at startup, but DPDK will do it on its own when the first vhost
> client is started.
> 
> Figuring out the reason why this happens kept me puzzled for quite some time...
> What happens is that the callbacks called from the vhost thread are
> calling ovsrcu_synchronize() as part of destroy_device(). This will
> end-up calling seq_wait__().
> 
> By default, all created threads outside of OVS will get thread id 0,
> which is equal to the main ovs thread. So for example in the
> seq_wait__() function above if the main thread is waiting already we
> won't add ourselves as a waiter.
> 
> The fix below assigns OVSTHREAD_ID_UNSET to none OVS created threads,
> which will get updated to a valid ID on the first call to
> ovsthread_id_self().
> 
> Signed-off-by: Eelco Chaudron <echaudro at redhat.com>


Fixes: f3e7ec254738 ("Update relevant artifacts to add support for DPDK 17.05.1.")
Acked-by: Ilya Maximets <i.maximets at samsung.com>


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