On 2015-09-30 15:09, Richard Henderson wrote: > By putting the prologue at the end, we risk overwriting the > prologue should our estimate of maximum TB size. Given the > two different placements of the call to tcg_prologue_init, > move the high water mark computation into tcg_prologue_init. > > Reviewed-by: Peter Maydell <peter.mayd...@linaro.org> > Signed-off-by: Richard Henderson <r...@twiddle.net> > --- > tcg/tcg.c | 35 ++++++++++++++++++++++++++++------- > translate-all.c | 28 +++++++++------------------- > 2 files changed, 37 insertions(+), 26 deletions(-)
Good idea to move it. I have done some experiments with putting slow path "helpers" in the prologue, and I ended-up going over the 1024 bytes limits. > diff --git a/tcg/tcg.c b/tcg/tcg.c > index d3693b1..5609108 100644 > --- a/tcg/tcg.c > +++ b/tcg/tcg.c > @@ -363,17 +363,38 @@ void tcg_context_init(TCGContext *s) > > void tcg_prologue_init(TCGContext *s) > { > - /* init global prologue and epilogue */ > - s->code_buf = s->code_gen_prologue; > - s->code_ptr = s->code_buf; > + size_t prologue_size, total_size; > + void *buf0, *buf1; > + > + /* Put the prologue at the beginning of code_gen_buffer. */ > + buf0 = s->code_gen_buffer; > + s->code_ptr = buf0; > + s->code_buf = buf0; > + s->code_gen_prologue = buf0; > + > + /* Generate the prologue. */ > tcg_target_qemu_prologue(s); > - flush_icache_range((uintptr_t)s->code_buf, (uintptr_t)s->code_ptr); > + buf1 = s->code_ptr; > + flush_icache_range((uintptr_t)buf0, (uintptr_t)buf1); > + > + /* Deduct the prologue from the buffer. */ > + prologue_size = tcg_current_code_size(s); > + s->code_gen_ptr = buf1; > + s->code_gen_buffer = buf1; > + s->code_buf = buf1; > + total_size = s->code_gen_buffer_size - prologue_size; > + s->code_gen_buffer_size = total_size; > + > + /* Compute a high-water mark, at which we voluntarily flush the > + buffer and start over. */ > + s->code_gen_buffer_max_size = total_size - TCG_MAX_OP_SIZE * > OPC_BUF_SIZE; > + > + tcg_register_jit(s->code_gen_buffer, total_size); I am not sure why you moved this 2 lines there, I think they have more their place in code_gen_alloc() so that the heuristics stay at the same place. total_size is available in s->code_gen_buffer_size, so that should be doable. > #ifdef DEBUG_DISAS > if (qemu_loglevel_mask(CPU_LOG_TB_OUT_ASM)) { > - size_t size = tcg_current_code_size(s); > - qemu_log("PROLOGUE: [size=%zu]\n", size); > - log_disas(s->code_buf, size); > + qemu_log("PROLOGUE: [size=%zu]\n", prologue_size); > + log_disas(buf0, prologue_size); > qemu_log("\n"); > qemu_log_flush(); > } > diff --git a/translate-all.c b/translate-all.c > index 3454f4e..0e8d176 100644 > --- a/translate-all.c > +++ b/translate-all.c > @@ -690,23 +690,15 @@ static inline void code_gen_alloc(size_t tb_size) > } > > qemu_madvise(tcg_ctx.code_gen_buffer, tcg_ctx.code_gen_buffer_size, > - QEMU_MADV_HUGEPAGE); > - > - /* Steal room for the prologue at the end of the buffer. This ensures > - (via the MAX_CODE_GEN_BUFFER_SIZE limits above) that direct branches > - from TB's to the prologue are going to be in range. It also means > - that we don't need to mark (additional) portions of the data segment > - as executable. */ > - tcg_ctx.code_gen_prologue = tcg_ctx.code_gen_buffer + > - tcg_ctx.code_gen_buffer_size - 1024; > - tcg_ctx.code_gen_buffer_size -= 1024; > - > - tcg_ctx.code_gen_buffer_max_size = tcg_ctx.code_gen_buffer_size - > - (TCG_MAX_OP_SIZE * OPC_BUF_SIZE); > - tcg_ctx.code_gen_max_blocks = tcg_ctx.code_gen_buffer_size / > - CODE_GEN_AVG_BLOCK_SIZE; > - tcg_ctx.tb_ctx.tbs = > - g_malloc(tcg_ctx.code_gen_max_blocks * sizeof(TranslationBlock)); > + QEMU_MADV_HUGEPAGE); > + > + /* Estimate a good size for the number of TBs we can support. We > + still haven't deducted the prologue from the buffer size here, > + but that's minimal and won't affect the estimate much. */ > + tcg_ctx.code_gen_max_blocks > + = tcg_ctx.code_gen_buffer_size / CODE_GEN_AVG_BLOCK_SIZE; > + tcg_ctx.tb_ctx.tbs = g_new(TranslationBlock, > tcg_ctx.code_gen_max_blocks); > + > qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock); > } > > @@ -717,8 +709,6 @@ void tcg_exec_init(unsigned long tb_size) > { > cpu_gen_init(); > code_gen_alloc(tb_size); > - tcg_ctx.code_gen_ptr = tcg_ctx.code_gen_buffer; > - tcg_register_jit(tcg_ctx.code_gen_buffer, tcg_ctx.code_gen_buffer_size); > page_init(); > #if defined(CONFIG_SOFTMMU) > /* There's no guest base to take into account, so go ahead and Otherwise the patch looks fine to me. -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurel...@aurel32.net http://www.aurel32.net