[ovs-dev] [PATCH] netdev-dpdk: Fix Tx queue false sharing.

Ilya Maximets i.maximets at ovn.org
Wed Oct 23 10:01:05 UTC 2019

On 12.09.2019 15:07, Eelco Chaudron wrote:
> On 26 Aug 2019, at 16:54, Ilya Maximets wrote:
>> 'tx_q' array is allocated for each DPDK netdev.  'struct dpdk_tx_queue'
>> is 8 bytes long, so 8 tx queues are sharing the same cache line in
>> case of 64B cacheline size.  This causes 'false sharing' issue in
>> mutliqueue case because taking the spinlock implies write to memory
>> i.e. cache invalidation.
>> Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
>> ---
>> I didn't really test the performance impact yet, so testing is very
>> welcome.  Relevant test case could be PVP with 8 queues in HW NIC and
>> 8 queues in vhost-user inerface and 8 PMD threads.
> Did a quick test on my setup, but I do not have enough cores to do 8 PMD threads and 8 VM cores. So I did a 4 core PMD/VM test running PV (not PVP as we do not care about receiving traffic from the VHOST) using 64 bytes packets and 100 L3 flows.
> Without the patch, I get 17,408,585 pps and with the patch 17,573,089 pps.
> The patch looks good to me…
> Acked-by: Eelco Chaudron <echaudro at redhat.com>

Thanks!  I'm expecting better results with more queues, but
it's a good improvement for 4 queues too.

Applied to master.

Best regards, Ilya Maximets.

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