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- Ask the firmware for the number of frames that can be stuffed in one
work request.
- Modify mp_ring to increase the likelihood of tx coalescing when there
are just one or two threads that are doing most of the tx. Add teeth
to the abdication mechanism by pushing the consumer lock into mp_ring.
This reduces the likelihood that a consumer will get stuck with all
the work even though it is above its budget.
- Add support for coalesced tx WR to the VF driver. This, with the
changes above, results in a 7x improvement in the tx pps of the VF
driver for some common cases. The firmware vets the L2 headers
submitted by the VF driver and it's a big win if the checks are
performed for a batch of packets and not each one individually.
Reviewed by: jhb@
MFC after: 2 weeks
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D25454
Notes:
svn path=/head/; revision=362905
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Suggested by: mjg@
MFC after: 1 month
Sponsored by: Chelsio Communications
Notes:
svn path=/head/; revision=338254
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Most affect comments, very few have user-visible effects.
Notes:
svn path=/head/; revision=298955
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of i386 systems.
Notes:
svn path=/head/; revision=277226
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a) Front load as much work as possible in if_transmit, before any driver
lock or software queue has to get involved.
b) Replace buf_ring with a brand new mp_ring (multiproducer ring). This
is specifically for the tx multiqueue model where one of the if_transmit
producer threads becomes the consumer and other producers carry on as
usual. mp_ring is implemented as standalone code and it should be
possible to use it in any driver with tx multiqueue. It also has:
- the ability to enqueue/dequeue multiple items. This might become
significant if packet batching is ever implemented.
- an abdication mechanism to allow a thread to give up writing tx
descriptors and have another if_transmit thread take over. A thread
that's writing tx descriptors can end up doing so for an unbounded
time period if a) there are other if_transmit threads continuously
feeding the sofware queue, and b) the chip keeps up with whatever the
thread is throwing at it.
- accurate statistics about interesting events even when the stats come
at the expense of additional branches/conditional code.
The NIC txq lock is uncontested on the fast path at this point. I've
left it there for synchronization with the control events (interface
up/down, modload/unload).
c) Add support for "type 1" coalescing work request in the normal NIC tx
path. This work request is optimized for frames with a single item in
the DMA gather list. These are very common when forwarding packets.
Note that netmap tx in cxgbe already uses these "type 1" work requests.
d) Do not request automatic cidx updates every 32 descriptors. Instead,
request updates via bits in individual work requests (still every 32
descriptors approximately). Also, request an automatic final update
when the queue idles after activity. This means NIC tx reclaim is still
performed lazily but it will catch up quickly as soon as the queue
idles. This seems to be the best middle ground and I'll probably do
something similar for netmap tx as well.
e) Implement a faster tx path for WRQs (used by TOE tx and control
queues, _not_ by the normal NIC tx). Allow work requests to be written
directly to the hardware descriptor ring if room is available. I will
convert t4_tom and iw_cxgbe modules to this faster style gradually.
MFC after: 2 months
Notes:
svn path=/head/; revision=276485
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