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...the #define headers as Rusty indicated and increasing the buffer size slightly by VirtioNet header size bytes per Eric. Jason, I'll followup with you directly - I'd like to know your exact workload (single steam or multi-stream netperf?), VM configuration, etc, and also see if the nit that Erichas pointed out affects your results. It is also worth noting that we may want to tune the queue sizes for your benchmarks, e.g, by reducing buffer size from 4KB to MTU-sized but keeping queue length constant, we're implicitly decreasing the number of bytes stored in the VirtioQueue for the Virtio...

...the #define headers as Rusty indicated and increasing the buffer size slightly by VirtioNet header size bytes per Eric. Jason, I'll followup with you directly - I'd like to know your exact workload (single steam or multi-stream netperf?), VM configuration, etc, and also see if the nit that Erichas pointed out affects your results. It is also worth noting that we may want to tune the queue sizes for your benchmarks, e.g, by reducing buffer size from 4KB to MTU-sized but keeping queue length constant, we're implicitly decreasing the number of bytes stored in the VirtioQueue for the Virtio...

The virtio_net driver's mergeable receive buffer allocator uses 4KB packet buffers. For MTU-sized traffic, SKB truesize is > 4KB but only ~1500 bytes of the buffer is used to store packet data, reducing the effective TCP window size substantially. This patch addresses the performance concerns with mergeable receive buffers by allocating MTU-sized packet buffers using page frag allocators.

The virtio_net driver's mergeable receive buffer allocator uses 4KB packet buffers. For MTU-sized traffic, SKB truesize is > 4KB but only ~1500 bytes of the buffer is used to store packet data, reducing the effective TCP window size substantially. This patch addresses the performance concerns with mergeable receive buffers by allocating MTU-sized packet buffers using page frag allocators.