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sfc: Only use TX push if a single descriptor is to be written
Using TX push when notifying the NIC of multiple new descriptors in the ring will very occasionally cause the TX DMA engine to re-use an old descriptor. This can result in a duplicated or partly duplicated packet (new headers with old data), or an IOMMU page fault. This does not happen when the pushed descriptor is the only one written. TX push also provides little latency benefit when a packet requires more than one descriptor. Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
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1 changed files with 2 additions and 1 deletions
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@ -376,7 +376,8 @@ efx_may_push_tx_desc(struct efx_tx_queue *tx_queue, unsigned int write_count)
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return false;
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tx_queue->empty_read_count = 0;
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return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0;
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return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0
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&& tx_queue->write_count - write_count == 1;
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}
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/* For each entry inserted into the software descriptor ring, create a
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