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doc: update faq

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Added some of the questions posted to the mailing list to the FAQ section of release notes.

Signed-off-by: Siobhan Butler <siobhan.a.butler@intel.com>
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Siobhan Butler 2015-03-22 13:25:07 +00:00 committed by Thomas Monjalon
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doc/guides/rel_notes/faq.rst
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@ -191,3 +191,38 @@ In this case, this has to be done manually on the VM host, using the following c
where <interface> being the interface providing the virtual functions for example, eth0, <VF function> being the virtual function number, for example 0,
and <MAC address> being the desired MAC address.
Is it safe to add an entry to the hash table while running?
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Currently the table implementation is not a thread safe implementation and assumes that locking between threads and processes is handled by the user's application.
This is likely to be supported in future releases.
What is the purpose of setting iommu=pt?
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DPDK uses a 1:1 mapping and does not support IOMMU. IOMMU allows for simpler VM physical address translation.
The second role of IOMMU is to allow protection from unwanted memory access by an unsafe device that has DMA privileges.
Unfortunately, the protection comes with an extremely high perfomance cost for high speed NICs.
iommu=pt disables IOMMU support for the hypervisor.
When trying to send packets from an application to itself, meaning smac==dmac, using Intel(R) 82599 VF packets are lost.
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Check on register LLE(PFVMTXSSW[n]), which allows an individual pool to send traffic and have it looped back to itself.
Can I split packet RX to use DPDK and have an application's higher order functions continue using Linux* pthread?
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The DPDK's lcore threads are Linux* pthreads bound onto specific cores. Configure the DPDK to do work on the same
cores and run the application's other work on other cores using the DPDK's "coremask" setting to specify which
cores it should launch itself on.
Is it possible to exchange data between DPDK processes and regular userspace processes via some shared memory or IPC mechanism?
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Yes - DPDK processes are regular Linux/BSD processes, and can use all OS provided IPC mechanisms.
Can the multiple queues in Intel(R) I350 be used with DPDK?
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I350 has RSS support and 8 queue pairs can be used in RSS mode. It should work with multi-queue DPDK applications using RSS.
How can hugepage-backed memory be shared among multiple processes?
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See the Primary and Secondary examples in the multi-process sample application.