[dpdk-dev] [PATCH] doc: add known issue for virtio TSO with clones
Olivier Matz
olivier.matz at 6wind.com
Mon Feb 6 14:16:53 CET 2017
Document the issue with Tso on shared packets.
Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
---
doc/guides/rel_notes/known_issues.rst | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/doc/guides/rel_notes/known_issues.rst b/doc/guides/rel_notes/known_issues.rst
index 018e999..f149ac7 100644
--- a/doc/guides/rel_notes/known_issues.rst
+++ b/doc/guides/rel_notes/known_issues.rst
@@ -666,3 +666,34 @@ uio pci generic module bind failed in X710/XL710/XXV710
**Driver/Module**:
Poll Mode Driver (PMD).
+
+
+virtio tx_burst() function cannot do TSO on shared packets
+----------------------------------------------------------
+
+**Description**:
+ The standard TX function of virtio driver does not manage shared
+ packets properly when doing TSO. These packets should be read-only
+ but the driver modifies them.
+
+ When doing TSO, the virtio standard expects that the L4 checksum is
+ set to the pseudo header checksum in the packet data, which is
+ different than the DPDK API. The driver patches the L4 checksum to
+ conform to the virtio standard, but this solution is invalid when
+ dealing with shared packets (clones), because the packet data should
+ not be modified.
+
+**Implication**:
+ In this situation, the shared data will be modified by the driver,
+ potentially causing race conditions with the other users of the mbuf
+ data.
+
+**Resolution/Workaround**:
+ The workaround in the application is to ensure that the network
+ headers in the packet data are not shared.
+
+**Affected Environment/Platform**:
+ Virtual machines running a virtio driver.
+
+**Driver/Module**:
+ Poll Mode Driver (PMD).
--
2.8.1
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