| Message ID | 20220905170125.1269498-1-vladimir.oltean@nxp.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Fixes for Felix DSA driver calculation of tc-taprio guard bands | expand |
Hello: This series was applied to netdev/net.git (master) by David S. Miller <davem@davemloft.net>: On Mon, 5 Sep 2022 20:01:22 +0300 you wrote: > This series fixes some bugs which are not quite new, but date from v5.13 > when static guard bands were enabled by Michael Walle to prevent > tc-taprio overruns. > > The investigation started when Xiaoliang asked privately what is the > expected max SDU for a traffic class when its minimum gate interval is > 10 us. The answer, as it turns out, is not an L1 size of 1250 octets, > but 1245 octets, since otherwise, the switch will not consider frames > for egress scheduling, because the static guard band is exactly as large > as the time interval. The switch needs a minimum of 33 ns outside of the > guard band to consider a frame for scheduling, and the reduction of the > max SDU by 5 provides exactly for that. > > [...] Here is the summary with links: - [v2,net,1/3] net: dsa: felix: tc-taprio intervals smaller than MTU should send at least one packet https://git.kernel.org/netdev/net/c/11afdc6526de - [v2,net,2/3] net: dsa: felix: disable cut-through forwarding for frames oversized for tc-taprio https://git.kernel.org/netdev/net/c/843794bbdef8 - [v2,net,3/3] net: dsa: felix: access QSYS_TAG_CONFIG under tas_lock in vsc9959_sched_speed_set https://git.kernel.org/netdev/net/c/a4bb481aeb9d You are awesome, thank you!
This series fixes some bugs which are not quite new, but date from v5.13 when static guard bands were enabled by Michael Walle to prevent tc-taprio overruns. The investigation started when Xiaoliang asked privately what is the expected max SDU for a traffic class when its minimum gate interval is 10 us. The answer, as it turns out, is not an L1 size of 1250 octets, but 1245 octets, since otherwise, the switch will not consider frames for egress scheduling, because the static guard band is exactly as large as the time interval. The switch needs a minimum of 33 ns outside of the guard band to consider a frame for scheduling, and the reduction of the max SDU by 5 provides exactly for that. The fix for that (patch 1/3) is relatively small, but during testing, it became apparent that cut-through forwarding prevents oversized frame dropping from working properly. This is solved through the larger patch 2/3. Finally, patch 3/3 fixes one more tc-taprio locking problem found through code inspection. Vladimir Oltean (3): net: dsa: felix: tc-taprio intervals smaller than MTU should send at least one packet net: dsa: felix: disable cut-through forwarding for frames oversized for tc-taprio net: dsa: felix: access QSYS_TAG_CONFIG under tas_lock in vsc9959_sched_speed_set drivers/net/dsa/ocelot/felix_vsc9959.c | 161 +++++++++++++++++-------- 1 file changed, 112 insertions(+), 49 deletions(-)