From: Luke Kenneth Casson Leighton Date: Sat, 25 May 2019 12:34:11 +0000 (+0100) Subject: experimenting with branch shadowing X-Git-Tag: div_pipeline~1947 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=2fc1c8f75c643b628423d03ff50486e2a3d09060;p=soc.git experimenting with branch shadowing --- diff --git a/src/experiment/score6600.py b/src/experiment/score6600.py index 626e8558..c7a36b26 100644 --- a/src/experiment/score6600.py +++ b/src/experiment/score6600.py @@ -15,7 +15,7 @@ from compalu import ComputationUnitNoDelay from alu_hier import ALU, BranchALU from nmutil.latch import SRLatch -from random import randint +from random import randint, seed class CompUnits(Elaboratable): @@ -269,7 +269,8 @@ class Scoreboard(Elaboratable): # Shadow Matrix. currently n_int_fus shadows, to be used for # write-after-write hazards. NOTE: there is one extra for branches, # so the shadow width is increased by 1 - m.submodules.shadows = shadows = ShadowMatrix(n_int_fus, n_int_fus+1) + m.submodules.shadows = shadows = ShadowMatrix(n_int_fus, n_int_fus) + m.submodules.bshadow = bshadow = ShadowMatrix(n_int_fus, 1) # combined go_rd/wr + go_die (go_die used to reset latches) go_rd_rst = Signal(n_int_fus, reset_less=True) @@ -348,15 +349,19 @@ class Scoreboard(Elaboratable): # connected to the FUReg and FUFU Matrices, to get them to reset # NOTE: do NOT connect these to the Computation Units. The CUs need to # do something slightly different (due to the revolving-door SRLatches) - comb += go_rd_rst.eq(go_rd_o | shadows.go_die_o) - comb += go_wr_rst.eq(go_wr_o | shadows.go_die_o) + anydie = Signal(n_int_fus, reset_less=True) + allshadown = Signal(n_int_fus, reset_less=True) + comb += allshadown.eq(shadows.shadown_o & bshadow.shadown_o) + comb += anydie.eq(shadows.go_die_o | bshadow.go_die_o) + comb += go_rd_rst.eq(go_rd_o | anydie) + comb += go_wr_rst.eq(go_wr_o | anydie) #--------- # NOTE; this setup is for the instruction order preservation... # connect shadows / go_dies to Computation Units - comb += cu.shadown_i[0:n_int_fus].eq(shadows.shadown_o[0:n_int_fus]) - comb += cu.go_die_i[0:n_int_fus].eq(shadows.go_die_o[0:n_int_fus]) + comb += cu.shadown_i[0:n_int_fus].eq(allshadown) + comb += cu.go_die_i[0:n_int_fus].eq(anydie) # ok connect first n_int_fu shadows to busy lines, to create an # instruction-order linked-list-like arrangement, using a bit-matrix @@ -364,7 +369,8 @@ class Scoreboard(Elaboratable): # XXX TODO # when written, the shadow can be cancelled (and was good) - comb += shadows.s_good_i[0:n_int_fus].eq(go_wr_o[0:n_int_fus]) + for i in range(n_int_fus): + comb += shadows.s_good_i[i][0:n_int_fus].eq(go_wr_o[0:n_int_fus]) # work out the current-activated busy unit (by recording the old one) with m.If(fn_issue_o): # only update prev bit if instruction issued @@ -381,33 +387,37 @@ class Scoreboard(Elaboratable): # tacked onto the ShadowMatrix (hence shadow_wid=n_int_fus+1) # only needs to set shadow_i, s_fail_i and s_good_i + # issue captures shadow_i (if enabled) + comb += bshadow.issue_i.eq(fn_issue_o) + + # instruction being issued (fn_issue_o) has a shadow cast by the branch with m.If(self.branch_succ_i | self.branch_fail_i): - comb += shadows.shadow_i[fn_issue_o][n_int_fus].eq(1) + comb += bshadow.shadow_i[fn_issue_o][0].eq(1) # finally, we need an indicator to the test infrastructure as to # whether the branch succeeded or failed, plus, link up to the # "recorder" of whether the instruction was under shadow or not with m.If(cu.br1.issue_i): - sync += bspec.issue_i.eq(1) - comb += bspec.good_i.eq(self.branch_succ_i) - comb += bspec.fail_i.eq(self.branch_fail_i) + sync += bspec.active_i.eq(1) + with m.If(self.branch_succ_i): + comb += bspec.good_i.eq(fn_issue_o & 0xf) + with m.If(self.branch_fail_i): + comb += bspec.fail_i.eq(fn_issue_o & 0xf) + # branch is active (TODO: a better signal: this is over-using the # go_write signal - actually the branch should not be "writing") with m.If(cu.br1.go_wr_i): sync += self.branch_direction_o.eq(cu.br1.data_o+Const(1, 2)) - sync += bspec.issue_i.eq(0) + sync += bspec.active_i.eq(0) comb += bspec.br_i.eq(1) # branch occurs if data == 1, failed if data == 0 - br_good = Signal(reset_less=True) - comb += br_good.eq(cu.br1.data_o == 1) - comb += bspec.br_good_i.eq(br_good) - comb += bspec.br_fail_i.eq(~br_good) - # the *expected* direction of the branch matched against *actual* - comb += shadows.s_good_i[n_int_fus].eq(bspec.matched_o) - # ... or it didn't - comb += shadows.s_fail_i[n_int_fus].eq(~bspec.matched_o) - + comb += bspec.br_ok_i.eq(cu.br1.data_o == 1) + for i in range(n_int_fus): + # *expected* direction of the branch matched against *actual* + comb += bshadow.s_good_i[i][0].eq(bspec.match_g_o[i]) + # ... or it didn't + comb += bshadow.s_fail_i[i][0].eq(bspec.match_f_o[i]) #--------- # Connect Register File(s) @@ -532,7 +542,7 @@ def create_random_ops(dut, n_ops, shadowing=False, max_opnums=3): op = randint(0, max_opnums) if shadowing: - insts.append((src1, src2, dest, op, (False, False))) + insts.append((src1, src2, dest, op, (0, 0))) else: insts.append((src1, src2, dest, op)) return insts @@ -562,6 +572,8 @@ def wait_for_issue(dut): def scoreboard_branch_sim(dut, alusim): + seed(0) + yield dut.int_store_i.eq(1) for i in range(2): @@ -574,14 +586,15 @@ def scoreboard_branch_sim(dut, alusim): alusim.setval(i, val) # create some instructions: branches create a tree - insts = create_random_ops(dut, 5) + insts = create_random_ops(dut, 1, True) src1 = randint(1, dut.n_regs-1) src2 = randint(1, dut.n_regs-1) - op = randint(4, 7) + #op = randint(4, 7) + op = 4 # only BGT at the moment - branch_ok = create_random_ops(dut, 5) - branch_fail = create_random_ops(dut, 5) + branch_ok = create_random_ops(dut, 1, True) + branch_fail = create_random_ops(dut, 1, True) insts.append((src1, src2, (branch_ok, branch_fail), op, (0, 0))) @@ -599,7 +612,7 @@ def scoreboard_branch_sim(dut, alusim): is_branch = op >= 4 if is_branch: branch_ok, branch_fail = dest - dest = None + dest = -1 # ok zip up the branch success / fail instructions and # drop them into the queue, one marked "to have branch success" # the other to be marked shadow branch "fail". @@ -612,7 +625,7 @@ def scoreboard_branch_sim(dut, alusim): shadow_on, shadow_off) yield yield from wait_for_issue(dut) - branch_direction = dut.branch_direction_o # which way branch went + branch_direction = yield dut.branch_direction_o # way branch went # wait for all instructions to stop before checking yield @@ -650,8 +663,8 @@ def scoreboard_sim(dut, alusim): # create some instructions (some random, some regression tests) instrs = [] - if False: - instrs = create_random_ops(dut, 10, False, 4) + if True: + instrs = create_random_ops(dut, 10, True, 4) if False: instrs.append((2, 3, 3, 0)) @@ -706,7 +719,16 @@ def scoreboard_sim(dut, alusim): instrs.append( (2, 6, 3, 0) ) instrs.append( (4, 2, 2, 1) ) - if True: + if False: + v1 = 4 + yield dut.intregs.regs[5].reg.eq(v1) + alusim.setval(5, v1) + yield dut.intregs.regs[3].reg.eq(5) + alusim.setval(3, 5) + instrs.append((5, 3, 3, 4, (0, 0))) + instrs.append((4, 2, 1, 2, (0, 1))) + + if False: v1 = 6 yield dut.intregs.regs[5].reg.eq(v1) alusim.setval(5, v1) @@ -740,7 +762,10 @@ def test_scoreboard(): with open("test_scoreboard6600.il", "w") as f: f.write(vl) - run_simulation(dut, scoreboard_sim(dut, alusim), + #run_simulation(dut, scoreboard_sim(dut, alusim), + # vcd_name='test_scoreboard6600.vcd') + + run_simulation(dut, scoreboard_branch_sim(dut, alusim), vcd_name='test_scoreboard6600.vcd') diff --git a/src/scoreboard/shadow.py b/src/scoreboard/shadow.py index d04c8e55..cd4089d7 100644 --- a/src/scoreboard/shadow.py +++ b/src/scoreboard/shadow.py @@ -118,9 +118,10 @@ class ShadowMatrix(Elaboratable): self.issue_i = Signal(n_fus, reset_less=True) self.shadow_i = Array(Signal(shadow_wid, name="sh_i", reset_less=True) \ for f in range(n_fus)) - self.s_fail_i = Signal(shadow_wid, reset_less=True) - self.s_good_i = Signal(shadow_wid, reset_less=True) - + self.s_fail_i = Array(Signal(shadow_wid, name="fl_i", reset_less=True) \ + for f in range(n_fus)) + self.s_good_i = Array(Signal(shadow_wid, name="gd_i", reset_less=True) \ + for f in range(n_fus)) # outputs self.go_die_o = Signal(n_fus, reset_less=True) self.shadown_o = Signal(n_fus, reset_less=True) @@ -133,8 +134,8 @@ class ShadowMatrix(Elaboratable): setattr(m.submodules, "sh%d" % i, sh) shadows.append(sh) # connect shadow/fail/good to all shadows - m.d.comb += sh.s_fail_i.eq(self.s_fail_i) - m.d.comb += sh.s_good_i.eq(self.s_good_i) + m.d.comb += sh.s_fail_i.eq(self.s_fail_i[i]) + m.d.comb += sh.s_good_i.eq(self.s_good_i[i]) # this one is the matrix (shadow enables) m.d.comb += sh.shadow_i.eq(self.shadow_i[i]) @@ -155,8 +156,8 @@ class ShadowMatrix(Elaboratable): def __iter__(self): yield self.issue_i yield from self.shadow_i - yield self.s_fail_i - yield self.s_good_i + yield from self.s_fail_i + yield from self.s_good_i yield self.go_die_o yield self.shadown_o @@ -182,44 +183,54 @@ class BranchSpeculationRecord(Elaboratable): self.n_fus = n_fus # inputs: record *expected* status - self.issue_i = Signal(reset_less=True) - self.good_i = Signal(reset_less=True) - self.fail_i = Signal(reset_less=True) + self.active_i = Signal(reset_less=True) + self.good_i = Signal(n_fus, reset_less=True) + self.fail_i = Signal(n_fus, reset_less=True) # inputs: status of branch (when result was known) self.br_i = Signal(reset_less=True) - self.br_good_i = Signal(reset_less=True) - self.br_fail_i = Signal(reset_less=True) + self.br_ok_i = Signal(reset_less=True) # outputs: true if the *expected* outcome matched the *actual* outcome - self.matched_o = Signal(reset_less=True) + self.match_f_o = Signal(n_fus, reset_less=True) + self.match_g_o = Signal(n_fus, reset_less=True) def elaborate(self, platform): m = Module() # registers to record *expected* status - good_r = Signal() - fail_r = Signal() - - with m.If(self.br_i): - # we expected fail, return OK that fail was EXPECTED... OR... - # we expected good, return OK that good was EXPECTED - success = Signal(reset_less=True) - m.d.comb += success.eq((good_r & self.br_good_i) | \ - (fail_r & self.br_fail_i) ) - # ... but only set these where a good or fail *is* expected... - with m.If(good_r | fail_r): - m.d.comb += self.matched_o.eq(success) - m.d.sync += good_r.eq(0) # might be set if issue set as well - m.d.sync += fail_r.eq(0) # might be set if issue set as well - with m.If(self.issue_i): - m.d.sync += good_r.eq(good_r | self.good_i) - m.d.sync += fail_r.eq(fail_r | self.fail_i) + good_r = Signal(self.n_fus) + fail_r = Signal(self.n_fus) + + for i in range(self.n_fus): + with m.If(self.active_i): + m.d.sync += good_r[i].eq(good_r[i] | self.good_i[i]) + m.d.sync += fail_r[i].eq(fail_r[i] | self.fail_i[i]) + with m.If(self.br_i): + # we expected fail, return OK that fail was EXPECTED... OR... + # we expected good, return OK that good was EXPECTED + good = Signal(reset_less=True) + fail = Signal(reset_less=True) + with m.If(self.br_ok_i): + m.d.comb += good.eq(good_r[i]) + m.d.comb += fail.eq(fail_r[i]) + with m.Else(): + m.d.comb += good.eq(~good_r[i]) + m.d.comb += fail.eq(~fail_r[i]) + # ... but only set these where a good or fail *is* expected... + with m.If(good_r[i]): + m.d.comb += self.match_g_o[i].eq(self.br_ok_i) + m.d.comb += self.match_f_o[i].eq(~self.br_ok_i) + with m.If(fail_r[i]): + m.d.comb += self.match_f_o[i].eq(~self.br_ok_i) + m.d.comb += self.match_g_o[i].eq(self.br_ok_i) + m.d.sync += good_r[i].eq(0) # might be set if issue set as well + m.d.sync += fail_r[i].eq(0) # might be set if issue set as well return m def __iter__(self): - yield self.issue_i + yield self.active_i yield self.good_i yield self.fail_i yield self.br_i