From f6bb84d53110398f4899c19dab4e0fe9908ec060 Mon Sep 17 00:00:00 2001 From: Emilio G. Cota Date: Tue, 11 Jul 2017 17:33:33 -0400 Subject: tcg: consolidate TB lookups in tb_lookup__cpu_state This avoids duplicating code. cpu_exec_step will also use the new common function once we integrate parallel_cpus into tb->cflags. Note that in this commit we also fix a race, described by Richard Henderson during review. Think of this scenario with threads A and B: (A) Lookup succeeds for TB in hash without tb_lock (B) Sets the TB's tb->invalid flag (B) Removes the TB from tb_htable (B) Clears all CPU's tb_jmp_cache (A) Store TB into local tb_jmp_cache Given that order of events, (A) will keep executing that invalid TB until another flush of its tb_jmp_cache happens, which in theory might never happen. We can fix this by checking the tb->invalid flag every time we look up a TB from tb_jmp_cache, so that in the above scenario, next time we try to find that TB in tb_jmp_cache, we won't, and will therefore be forced to look it up in tb_htable. Performance-wise, I measured a small improvement when booting debian-arm. Note that inlining pays off: Performance counter stats for 'taskset -c 0 qemu-system-arm \ -machine type=virt -nographic -smp 1 -m 4096 \ -netdev user,id=unet,hostfwd=tcp::2222-:22 \ -device virtio-net-device,netdev=unet \ -drive file=jessie.qcow2,id=myblock,index=0,if=none \ -device virtio-blk-device,drive=myblock \ -kernel kernel.img -append console=ttyAMA0 root=/dev/vda1 \ -name arm,debug-threads=on -smp 1' (10 runs): Before: 18714.917392 task-clock # 0.952 CPUs utilized ( +- 0.95% ) 23,142 context-switches # 0.001 M/sec ( +- 0.50% ) 1 CPU-migrations # 0.000 M/sec 10,558 page-faults # 0.001 M/sec ( +- 0.95% ) 53,957,727,252 cycles # 2.883 GHz ( +- 0.91% ) [83.33%] 24,440,599,852 stalled-cycles-frontend # 45.30% frontend cycles idle ( +- 1.20% ) [83.33%] 16,495,714,424 stalled-cycles-backend # 30.57% backend cycles idle ( +- 0.95% ) [66.66%] 76,267,572,582 instructions # 1.41 insns per cycle # 0.32 stalled cycles per insn ( +- 0.87% ) [83.34%] 12,692,186,323 branches # 678.186 M/sec ( +- 0.92% ) [83.35%] 263,486,879 branch-misses # 2.08% of all branches ( +- 0.73% ) [83.34%] 19.648474449 seconds time elapsed ( +- 0.82% ) After, w/ inline (this patch): 18471.376627 task-clock # 0.955 CPUs utilized ( +- 0.96% ) 23,048 context-switches # 0.001 M/sec ( +- 0.48% ) 1 CPU-migrations # 0.000 M/sec 10,708 page-faults # 0.001 M/sec ( +- 0.81% ) 53,208,990,796 cycles # 2.881 GHz ( +- 0.98% ) [83.34%] 23,941,071,673 stalled-cycles-frontend # 44.99% frontend cycles idle ( +- 0.95% ) [83.34%] 16,161,773,848 stalled-cycles-backend # 30.37% backend cycles idle ( +- 0.76% ) [66.67%] 75,786,269,766 instructions # 1.42 insns per cycle # 0.32 stalled cycles per insn ( +- 1.24% ) [83.34%] 12,573,617,143 branches # 680.708 M/sec ( +- 1.34% ) [83.33%] 260,235,550 branch-misses # 2.07% of all branches ( +- 0.66% ) [83.33%] 19.340502161 seconds time elapsed ( +- 0.56% ) After, w/o inline: 18791.253967 task-clock # 0.954 CPUs utilized ( +- 0.78% ) 23,230 context-switches # 0.001 M/sec ( +- 0.42% ) 1 CPU-migrations # 0.000 M/sec 10,563 page-faults # 0.001 M/sec ( +- 1.27% ) 54,168,674,622 cycles # 2.883 GHz ( +- 0.80% ) [83.34%] 24,244,712,629 stalled-cycles-frontend # 44.76% frontend cycles idle ( +- 1.37% ) [83.33%] 16,288,648,572 stalled-cycles-backend # 30.07% backend cycles idle ( +- 0.95% ) [66.66%] 77,659,755,503 instructions # 1.43 insns per cycle # 0.31 stalled cycles per insn ( +- 0.97% ) [83.34%] 12,922,780,045 branches # 687.702 M/sec ( +- 1.06% ) [83.34%] 261,962,386 branch-misses # 2.03% of all branches ( +- 0.71% ) [83.35%] 19.700174670 seconds time elapsed ( +- 0.56% ) Reviewed-by: Richard Henderson Signed-off-by: Emilio G. Cota Signed-off-by: Richard Henderson --- include/exec/tb-lookup.h | 49 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 include/exec/tb-lookup.h (limited to 'include/exec/tb-lookup.h') diff --git a/include/exec/tb-lookup.h b/include/exec/tb-lookup.h new file mode 100644 index 0000000000..9d32cb0c6e --- /dev/null +++ b/include/exec/tb-lookup.h @@ -0,0 +1,49 @@ +/* + * Copyright (C) 2017, Emilio G. Cota + * + * License: GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ +#ifndef EXEC_TB_LOOKUP_H +#define EXEC_TB_LOOKUP_H + +#include "qemu/osdep.h" + +#ifdef NEED_CPU_H +#include "cpu.h" +#else +#include "exec/poison.h" +#endif + +#include "exec/exec-all.h" +#include "exec/tb-hash.h" + +/* Might cause an exception, so have a longjmp destination ready */ +static inline TranslationBlock * +tb_lookup__cpu_state(CPUState *cpu, target_ulong *pc, target_ulong *cs_base, + uint32_t *flags) +{ + CPUArchState *env = (CPUArchState *)cpu->env_ptr; + TranslationBlock *tb; + uint32_t hash; + + cpu_get_tb_cpu_state(env, pc, cs_base, flags); + hash = tb_jmp_cache_hash_func(*pc); + tb = atomic_rcu_read(&cpu->tb_jmp_cache[hash]); + if (likely(tb && + tb->pc == *pc && + tb->cs_base == *cs_base && + tb->flags == *flags && + tb->trace_vcpu_dstate == *cpu->trace_dstate && + !atomic_read(&tb->invalid))) { + return tb; + } + tb = tb_htable_lookup(cpu, *pc, *cs_base, *flags); + if (tb == NULL) { + return NULL; + } + atomic_set(&cpu->tb_jmp_cache[hash], tb); + return tb; +} + +#endif /* EXEC_TB_LOOKUP_H */ -- cgit v1.2.3-55-g7522