- Ever since the workaround for the silicon bug of TSO4 causing MAC hangs was committed in r295133, CSUM_TSO always got disabled unconditionally by em(4) on the first invocation of em_init_locked(). However, even with that problem fixed, it turned out that for at least e. g. 82579 not all necessary TSO workarounds are in place, still causing MAC hangs even at Gigabit speed. Thus, for stable/11, TSO usage was deliberately disabled in r323292 (r323293 for stable/10) for the EM-class by default, allowing users to turn it on if it happens to work with their particular EM MAC in a Gigabit-only environment. In head, the TSO workaround for speeds other than Gigabit was lost with the conversion to iflib(9) in r311849 (possibly along with another one or two TSO workarounds). Yet at the same time, for EM-class MACs TSO4 is enabled by default again, causing device hangs. Therefore, change the default for this hardware class back to have TSO4 off, allowing users to turn it on manually if it happens to work in their environment as we do in stable/{10,11}. An alternative would be to add a whitelist of EM-class devices where TSO4 actually is reliable with the workarounds in place, but given that the advantage of TSO at Gigabit speed is rather limited - especially with the overhead of these workarounds -, that's really not worth it. [1]
- Although 82543 support TSO4 in theory, the former lem(4) didn't have support for TSO4, presumably because TSO4 is even more broken in the LEM-class of MACs than the later EM ones. Still, TSO4 for LEM-class devices was enabled as part of the conversion to iflib(9) in r311849, causing device hangs. So revert back to the pre-r311849 behavior of not supporting TSO4 for LEM-class at all, which includes not creating a TSO DMA tag in iflib(9) for devices not having IFCAP_TSO4 set. [2]
- In fact, the FreeBSD TCP stack can handle a TSO size of IP_MAXPACKET (65535) rather than FREEBSD_TSO_SIZE_MAX (65518). However, the TSO DMA must have a maxsize of the maximum TSO size plus the size of a VLAN header for software VLAN tagging. The iflib(9) converted em(4), thus, first correctly sets scctx->isc_tx_tso_size_max to EM_TSO_SIZE in em_if_attach_pre(), but later on overrides it with IP_MAXPACKET in em_setup_interface() (apparently, left-over from pre-iflib(9) times). So remove the later and correct iflib(9) to correctly cap the maximum TSO size reported to the stack at IP_MAXPACKET. While at it, let iflib(9) use if_sethwtsomax*().
- Move the reduction of the maximum TSO segment count reported to the stack by the number of m_pullup(9) calls (which in the worst case, can add another mbuf and, thus, the requirement for another DMA segment each) in the transmit path for performance reasons from em_setup_interface() to iflib_txsd_alloc() as these pull-ups are now done in iflib_parse_header() rather than in the no longer existing em_xmit(). Moreover, this optimization applies to all drivers using iflib(9) and not just em(4); all in-tree iflib(9) consumers still have enough room to handle full size TSO packets. Also, reduce the adjustment to the maximum number of m_pullup(9)'s now performed in iflib_parse_header().
- Prior to the conversion to iflib(9) in r311849, em(4) didn't enable IFCAP_VLAN_HWFILTER by default due to VLAN events not being passed through by lagg(4). With iflib(9), IFCAP_VLAN_HWFILTER now is turned on by default but also lagg(4) was fixed in that regard in r203548. So just remove the now redundant and defunct IFCAP_VLAN_HWFILTER handling in em_setup_interface().
- Remove also other redundant IFCAP_* setting in em_setup_interface() which is (more completely) already done in em_if_attach_pre() now.
- Remove some redundant/dead setting of scctx->isc_tx_csum_flags in em_if_attach_pre().
- Remove some IFCAP_* duplicated either directly or indirectly (e. g. via IFCAP_HWCSUM) in {EM,IGB}_CAPS.
- Remove some unused macros from em(4).
Okayed by: sbruno@ at 201806 DevSummit Transport Working Group [1]
PR: 220997 (part of) [2]