Re: [ovs-dev] [PATCH v2 24/28] dpif-netdev: Use lockless queue to manage offloads

[Maxime Coquelin]

On 4/12/21 5:20 PM, Gaetan Rivet wrote:
> |The dataplane threads (PMDs) send offloading commands to a dedicated
> offload management thread. The current implementation uses a lock and
> benchmarks show a high contention on the queue in some cases. With
> high-contention, the mutex will more often lead to the locking thread
> yielding in wait, using a syscall. This should be avoided in a userland
> dataplane. The mpsc-queue can be used instead. It uses less cycles and
> has lower latency. Benchmarks show better behavior as multiple
> revalidators and one or multiple PMDs writes to a single queue while
> another thread polls it. One trade-off with the new scheme however is to
> be forced to poll the queue from the offload thread. Without mutex, a
> cond_wait cannot be used for signaling. The offload thread is
> implementing an exponential backoff and will sleep in short increments
> when no data is available. This makes the thread yield, at the price of
> some latency to manage offloads after an inactivity period.
> Signed-off-by: Gaetan Rivet <gr...@u256.net> Reviewed-by: Eli Britstein
> <el...@nvidia.com> --- lib/dpif-netdev.c | 109
> ++++++++++++++++++++++++---------------------- 1 file changed, 57
> insertions(+), 52 deletions(-)|

With the ovsrcu_quiesce()/next_rcu change discussed in patch 14:

Reviewed-by: Maxime Coquelin <maxime.coque...@redhat.com>

Thanks,
Maxime

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