Re: [Qemu-devel] [PATCH v2 1/4] add and link a statistic struct to TBs

[Vanderson Martins do Rosario]

When the tb_flush removes a block and it's recreated, this shouldn't
be creating a new block but using the one that is found by:

lookup_result = g_list_find_custom(tb_ctx.tb_statistics, new_stats,
statistics_cmp);

So the tb_statisticics will be reused and we could just add this
regen counter in the if statement: if (lookup_result)

isn't that correct?

Vanderson M. Rosario


On Tue, Jun 25, 2019 at 1:28 PM Alex Bennée <address@hidden> wrote:

>
> Alex Bennée <address@hidden> writes:
>
> > vandersonmr <address@hidden> writes:
> >
> >> We want to store statistics for each TB even after flushes.
> >> We do not want to modify or grow the TB struct.
> >> So we create a new struct to contain this statistics and
> >> link it to each TB while they are created.
> >>
> >> Signed-off-by: Vanderson M. do Rosario <address@hidden>
> >> ---
> >>  accel/tcg/translate-all.c | 40 +++++++++++++++++++++++++++++++++++++++
> >>  include/exec/exec-all.h   | 21 ++++++++++++++++++++
> >>  include/exec/tb-context.h |  1 +
> >>  include/qemu/log.h        |  1 +
> >>  4 files changed, 63 insertions(+)
> >>
> >> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> >> index 5d1e08b169..f7e99f90e0 100644
> >> --- a/accel/tcg/translate-all.c
> >> +++ b/accel/tcg/translate-all.c
> >> @@ -1118,6 +1118,18 @@ static inline void code_gen_alloc(size_t tb_size)
> >>      }
> >>  }
> >>
> >> +static gint statistics_cmp(gconstpointer p1, gconstpointer p2)
> >> +{
> >> +    const TBStatistics *a = (TBStatistics *) p1;
> >> +    const TBStatistics *b = (TBStatistics *) p2;
> >> +
> >> +    return (a->pc == b->pc &&
> >> +               a->cs_base == b->cs_base &&
> >> +               a->flags == b->flags &&
> >> +           a->page_addr[0] == b->page_addr[0] &&
> >> +               a->page_addr[1] == b->page_addr[1]) ? 0 : 1;
> >> +}
> >> +
> >
> > There are a bunch of white space errors that need fixing up as you
> > probably already know from patchew ;-)
> >
> >>  static bool tb_cmp(const void *ap, const void *bp)
> >>  {
> >>      const TranslationBlock *a = ap;
> >> @@ -1586,6 +1598,29 @@ static inline void tb_page_add(PageDesc *p,
> TranslationBlock *tb,
> >>  #endif
> >>  }
> >>
> >> +static void tb_insert_statistics_structure(TranslationBlock *tb) {
> >> +    TBStatistics *new_stats = g_new0(TBStatistics, 1);
> >> +    new_stats->pc = tb->pc;
> >> +    new_stats->cs_base = tb->cs_base;
> >> +    new_stats->flags = tb->flags;
> >> +    new_stats->page_addr[0] = tb->page_addr[0];
> >> +    new_stats->page_addr[1] = tb->page_addr[1];
> >> +
> >> +    GList *lookup_result = g_list_find_custom(tb_ctx.tb_statistics,
> new_stats, statistics_cmp);
> >> +
> >> +    if (lookup_result) {
> >> +            /* If there is already a TBStatistic for this TB from a
> previous flush
> >> +            * then just make the new TB point to the older TBStatistic
> >> +            */
> >> +            free(new_stats);
> >> +            tb->tb_stats = lookup_result->data;
> >> +    } else {
> >> +            /* If not, then points to the new tb_statistics and add it
> to the hash */
> >> +            tb->tb_stats = new_stats;
> >> +            tb_ctx.tb_statistics = g_list_prepend(tb_ctx.tb_statistics,
> >> new_stats);
> >
> > This is going to race as nothing prevents two threads attempting to
> > insert records at the same time.
> >
> >> +    }
> >> +}
> >> +
> >>  /* add a new TB and link it to the physical page tables. phys_page2 is
> >>   * (-1) to indicate that only one page contains the TB.
> >>   *
> >> @@ -1636,6 +1671,11 @@ tb_link_page(TranslationBlock *tb,
> tb_page_addr_t phys_pc,
> >>          void *existing_tb = NULL;
> >>          uint32_t h;
> >>
> >> +        if (qemu_loglevel_mask(CPU_LOG_HOT_TBS)) {
> >> +            /* create and link to its TB a structure to store
> statistics */
> >> +            tb_insert_statistics_structure(tb);
> >> +            }
> >> +
> >>          /* add in the hash table */
> >>          h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags &
> CF_HASH_MASK,
> >>                           tb->trace_vcpu_dstate);
> >
> > Perhaps we could just have a second qht array which allows for
> > "unlocked" insertion of record. You could take advantage of the fact the
> > hash would be the same:
> >
> >         h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags &
> CF_HASH_MASK,
> >                          tb->trace_vcpu_dstate);
> >         qht_insert(&tb_ctx.htable, tb, h, &existing_tb);
> >
> >         /* remove TB from the page(s) if we couldn't insert it */
> >         if (unlikely(existing_tb)) {
> >             ...
> >             tb = existing_tb;
> >         } else if (qemu_loglevel_mask(CPU_LOG_HOT_TBS)) {
> >             TBStatistics *new_stats = g_new0(TBStatistics, 1);
> >             bool ok;
> >             new_stats->pc = tb->pc;
> >             new_stats->cs_base = tb->cs_base;
> >             new_stats->flags = tb->flags;
> >             new_stats->page_addr[0] = tb->page_addr[0];
> >             new_stats->page_addr[1] = tb->page_addr[1];
> >             ok = qht_insert(&tb_ctx.tb_stats, new_stats, h, NULL);
> >             /*
> >              * This should never fail as we succeeded in inserting the
> >              * TB itself which means we haven't seen this combination
> yet.
> >              */
> >             g_assert(ok);
> >         }
> >
> > It would also avoid the clunkiness of having to allocate and then
> > freeing an unused structure.
>
>
> Actually thinking on this we still have to handle it. We may have
> tb_flushed away a translation and just be regenerating the same block.
> As TBStatistics should transcend tb_flush events we need to re-use it's
> structure.
>
> It would be worth counting the regens as well so we can see blocks that
> keep getting re-translated after each flush.
>
> >
> >> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> >> index 16034ee651..359100ef3b 100644
> >> --- a/include/exec/exec-all.h
> >> +++ b/include/exec/exec-all.h
> >> @@ -324,6 +324,24 @@ static inline void
> tlb_flush_by_mmuidx_all_cpus_synced(CPUState *cpu,
> >>  #define CODE_GEN_AVG_BLOCK_SIZE 150
> >>  #endif
> >>
> >> +typedef struct TBStatistics TBStatistics;
> >> +
> >> +/*
> >> + * This struct stores statistics such as execution count of the
> TranslationBlocks.
> >> + * Each TB has its own TBStatistics. TBStatistics is suppose to live
> even after
> >> + * flushes.
> >> + */
> >> +struct TBStatistics {
> >> +    target_ulong pc;
> >> +    target_ulong cs_base;
> >> +    uint32_t flags;
> >> +    tb_page_addr_t page_addr[2];
> >> +
> >> +    // total number of times that the related TB have being executed
> >
> > No c++ style comments
> >
> >> +    uint32_t exec_count;
> >> +    uint32_t exec_count_overflows;
> >> +};
> >> +
> >>  /*
> >>   * Translation Cache-related fields of a TB.
> >>   * This struct exists just for convenience; we keep track of TB's in a
> binary
> >> @@ -403,6 +421,9 @@ struct TranslationBlock {
> >>      uintptr_t jmp_list_head;
> >>      uintptr_t jmp_list_next[2];
> >>      uintptr_t jmp_dest[2];
> >> +
> >> +    // Pointer to a struct where statistics from the TB is stored
> >
> > No c++ style comments
> >
> >> +    TBStatistics *tb_stats;
> >>  };
> >>
> >>  extern bool parallel_cpus;
> >> diff --git a/include/exec/tb-context.h b/include/exec/tb-context.h
> >> index feb585e0a7..a78ce92e60 100644
> >> --- a/include/exec/tb-context.h
> >> +++ b/include/exec/tb-context.h
> >> @@ -35,6 +35,7 @@ struct TBContext {
> >>
> >>      /* statistics */
> >>      unsigned tb_flush_count;
> >> +    GList *tb_statistics;
> >>  };
> >>
> >>  extern TBContext tb_ctx;
> >> diff --git a/include/qemu/log.h b/include/qemu/log.h
> >> index b097a6cae1..2fca65dd01 100644
> >> --- a/include/qemu/log.h
> >> +++ b/include/qemu/log.h
> >> @@ -45,6 +45,7 @@ static inline bool qemu_log_separate(void)
> >>  /* LOG_TRACE (1 << 15) is defined in log-for-trace.h */
> >>  #define CPU_LOG_TB_OP_IND  (1 << 16)
> >>  #define CPU_LOG_TB_FPU     (1 << 17)
> >> +#define CPU_LOG_HOT_TBS    (1 << 18)
> >>
> >>  /* Lock output for a series of related logs.  Since this is not needed
> >>   * for a single qemu_log / qemu_log_mask / qemu_log_mask_and_addr, we
>
>
> --
> Alex Bennée
>