Re: [dpdk-dev] [PATCH] Do RCU synchronization at fixed interval in PMD main loop.

[David Marchand <david.marchand@redhat.com>]

Hello Nitin,

On Wed, Aug 7, 2019 at 8:13 AM Nitin Katiyar <nitin.katiyar@ericsson.com> wrote:
>
> Each PMD updates the global sequence number for RCU synchronization
> purpose with other OVS threads. This is done at every 1025th iteration
> in PMD main loop.
>
> If the PMD thread is responsible for polling large number of queues
> that are carrying traffic, it spends a lot of time processing packets
> and this results in significant delay in performing the housekeeping
> activities.
>
> If the OVS main thread is waiting to synchronize with the PMD threads
> and if those threads delay performing housekeeping activities for
> more than 3 sec then LACP processing will be impacted and it will lead
> to LACP flaps. Similarly, other controls protocols run by OVS main
> thread are impacted.
>
> For e.g. a PMD thread polling 200 ports/queues with average of 1600
> processing cycles per packet with batch size of 32 may take 10240000
> (200 * 1600 * 32) cycles per iteration. In system with 2.0 GHz CPU
> it means more than 5 ms per iteration. So, for 1024 iterations to
> complete it would be more than 5 seconds.
>
> This gets worse when there are PMD threads which are less loaded.
> It reduces possibility of getting mutex lock in ovsrcu_try_quiesce()
> by heavily loaded PMD and next attempt to quiesce would be after 1024
> iterations.
>
> With this patch, PMD RCU synchronization will be performed after fixed
> interval instead after a fixed number of iterations. This will ensure
> that even if the packet processing load is high the RCU synchronization
> will not be delayed long.
>
> Signed-off-by: Anju Thomas <anju.thomas@ericsson.com>
> Signed-off-by: Nitin Katiyar <nitin.katiyar@ericsson.com>
> ---
>  lib/dpif-netdev-perf.c | 16 ----------------
>  lib/dpif-netdev-perf.h | 17 +++++++++++++++++
>  lib/dpif-netdev.c      | 27 +++++++++++++++++++++++++++
>  3 files changed, 44 insertions(+), 16 deletions(-)

s/To: dev@dpdk.org/To: dev@openvswitch.org/



-- 
David Marchand