nfp: bpf: fix latency bug when updating stack index register
authorJiong Wang <jiong.wang@netronome.com>
Sat, 24 Aug 2019 02:00:28 +0000 (19:00 -0700)
committerDaniel Borkmann <daniel@iogearbox.net>
Mon, 26 Aug 2019 21:03:05 +0000 (23:03 +0200)
commit86c28b2d69f93a218a9a5cef146ed0097a98687f
treee07815a72b0c7b5ae1e287e9a5be88b9323056ac
parentf53a7ad189594a112167efaf17ea8d0242b5ac00
nfp: bpf: fix latency bug when updating stack index register

NFP is using Local Memory to model stack. LM_addr could be used as base of
a 16 32-bit word region of Local Memory. Then, if the stack offset is
beyond the current region, the local index needs to be updated. The update
needs at least three cycles to take effect, therefore the sequence normally
looks like:

  local_csr_wr[ActLMAddr3, gprB_5]
  nop
  nop
  nop

If the local index switch happens on a narrow loads, then the instruction
preparing value to zero high 32-bit of the destination register could be
counted as one cycle, the sequence then could be something like:

  local_csr_wr[ActLMAddr3, gprB_5]
  nop
  nop
  immed[gprB_5, 0]

However, we have zero extension optimization that zeroing high 32-bit could
be eliminated, therefore above IMMED insn won't be available for which case
the first sequence needs to be generated.

Fixes: 0b4de1ff19bf ("nfp: bpf: eliminate zero extension code-gen")
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
drivers/net/ethernet/netronome/nfp/bpf/jit.c