Re: [PATCH v5 12/50] perf map: Simplify map_ip/unmap_ip and make map size smaller

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Dec 04, 2023 at 03:39:08PM -0800, Namhyung Kim escreveu:
> Hi Ian,
> 
> On Mon, Nov 27, 2023 at 2:09 PM Ian Rogers <irogers@google.com> wrote:
> >
> > When mapping an IP it is either an identity mapping or a DSO relative
> > mapping, so a single bit is required in the struct to identify
> > this. The current code uses function pointers, adding 2 pointers per
> > map and also pushing the size of a map beyond 1 cache line. Switch to
> > using a byte to identify the mapping type (as well as priv and
> > erange_warned), to avoid any masking. Change struct maps's layout to
> > avoid holes.
> >
> > Before:
> > ```
> > struct map {
> >         u64                        start;                /*     0     8 */
> >         u64                        end;                  /*     8     8 */
> >         _Bool                      erange_warned:1;      /*    16: 0  1 */
> >         _Bool                      priv:1;               /*    16: 1  1 */
> >
> >         /* XXX 6 bits hole, try to pack */
> >         /* XXX 3 bytes hole, try to pack */
> >
> >         u32                        prot;                 /*    20     4 */
> >         u64                        pgoff;                /*    24     8 */
> >         u64                        reloc;                /*    32     8 */
> >         u64                        (*map_ip)(const struct map  *, u64); /*    40     8 */
> >         u64                        (*unmap_ip)(const struct map  *, u64); /*    48     8 */
> >         struct dso *               dso;                  /*    56     8 */
> >         /* --- cacheline 1 boundary (64 bytes) --- */
> >         refcount_t                 refcnt;               /*    64     4 */
> >         u32                        flags;                /*    68     4 */
> >
> >         /* size: 72, cachelines: 2, members: 12 */
> >         /* sum members: 68, holes: 1, sum holes: 3 */
> >         /* sum bitfield members: 2 bits, bit holes: 1, sum bit holes: 6 bits */
> >         /* last cacheline: 8 bytes */
> > };
> > ```
> >
> > After:
> > ```
> > struct map {
> >         u64                        start;                /*     0     8 */
> >         u64                        end;                  /*     8     8 */
> >         u64                        pgoff;                /*    16     8 */
> >         u64                        reloc;                /*    24     8 */
> >         struct dso *               dso;                  /*    32     8 */
> >         refcount_t                 refcnt;               /*    40     4 */
> >         u32                        prot;                 /*    44     4 */
> >         u32                        flags;                /*    48     4 */
> >         enum mapping_type          mapping_type:8;       /*    52: 0  4 */
> >
> >         /* Bitfield combined with next fields */
> >
> >         _Bool                      erange_warned;        /*    53     1 */
> >         _Bool                      priv;                 /*    54     1 */
> >
> >         /* size: 56, cachelines: 1, members: 11 */
> >         /* padding: 1 */
> >         /* last cacheline: 56 bytes */
> > };
> > ```
> 
> Thanks for doing this!  I really wanted to clean up the map
> code and to make it more intuitive.
> 
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> 
> Acked-by: Namhyung Kim <namhyung@kernel.org>

Applied
 
> A few nitpicks below.

Ian, please consider those for a follow up clarifying patch.

- Arnaldo
 
> > ---
> >  tools/perf/util/machine.c    |  3 +-
> >  tools/perf/util/map.c        | 20 +--------
> >  tools/perf/util/map.h        | 83 +++++++++++++++++++-----------------
> >  tools/perf/util/symbol-elf.c |  6 +--
> >  tools/perf/util/symbol.c     |  6 +--
> >  5 files changed, 50 insertions(+), 68 deletions(-)
> >
> > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > index be3dab9d5253..b6831a1f909d 100644
> > --- a/tools/perf/util/machine.c
> > +++ b/tools/perf/util/machine.c
> > @@ -1360,8 +1360,7 @@ __machine__create_kernel_maps(struct machine *machine, struct dso *kernel)
> >         if (machine->vmlinux_map == NULL)
> >                 return -ENOMEM;
> >
> > -       map__set_map_ip(machine->vmlinux_map, identity__map_ip);
> > -       map__set_unmap_ip(machine->vmlinux_map, identity__map_ip);
> > +       map__set_mapping_type(machine->vmlinux_map, MAPPING_TYPE__IDENTITY);
> >         return maps__insert(machine__kernel_maps(machine), machine->vmlinux_map);
> >  }
> >
> > diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> > index f64b83004421..54c67cb7ecef 100644
> > --- a/tools/perf/util/map.c
> > +++ b/tools/perf/util/map.c
> > @@ -109,8 +109,7 @@ void map__init(struct map *map, u64 start, u64 end, u64 pgoff, struct dso *dso)
> >         map__set_pgoff(map, pgoff);
> >         map__set_reloc(map, 0);
> >         map__set_dso(map, dso__get(dso));
> > -       map__set_map_ip(map, map__dso_map_ip);
> > -       map__set_unmap_ip(map, map__dso_unmap_ip);
> > +       map__set_mapping_type(map, MAPPING_TYPE__DSO);
> >         map__set_erange_warned(map, false);
> >         refcount_set(map__refcnt(map), 1);
> >  }
> > @@ -172,7 +171,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> >                 map__init(result, start, start + len, pgoff, dso);
> >
> >                 if (anon || no_dso) {
> > -                       map->map_ip = map->unmap_ip = identity__map_ip;
> > +                       map->mapping_type = MAPPING_TYPE__IDENTITY;
> >
> >                         /*
> >                          * Set memory without DSO as loaded. All map__find_*
> > @@ -630,18 +629,3 @@ struct maps *map__kmaps(struct map *map)
> >         }
> >         return kmap->kmaps;
> >  }
> > -
> > -u64 map__dso_map_ip(const struct map *map, u64 ip)
> > -{
> > -       return ip - map__start(map) + map__pgoff(map);
> > -}
> > -
> > -u64 map__dso_unmap_ip(const struct map *map, u64 ip)
> > -{
> > -       return ip + map__start(map) - map__pgoff(map);
> > -}
> > -
> > -u64 identity__map_ip(const struct map *map __maybe_unused, u64 ip)
> > -{
> > -       return ip;
> > -}
> > diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
> > index 1b53d53adc86..3a3b7757da5f 100644
> > --- a/tools/perf/util/map.h
> > +++ b/tools/perf/util/map.h
> > @@ -16,23 +16,25 @@ struct dso;
> >  struct maps;
> >  struct machine;
> >
> > +enum mapping_type {
> > +       /* map__map_ip/map__unmap_ip are given as offsets in the DSO. */
> > +       MAPPING_TYPE__DSO,
> 
> I slightly prefer __PIC than __DSO, but won't argue. :)
> 
> > +       /* map__map_ip/map__unmap_ip are just the given ip value. */
> > +       MAPPING_TYPE__IDENTITY,
> > +};
> > +
> >  DECLARE_RC_STRUCT(map) {
> >         u64                     start;
> >         u64                     end;
> > -       bool                    erange_warned:1;
> > -       bool                    priv:1;
> > -       u32                     prot;
> >         u64                     pgoff;
> >         u64                     reloc;
> > -
> > -       /* ip -> dso rip */
> > -       u64                     (*map_ip)(const struct map *, u64);
> > -       /* dso rip -> ip */
> > -       u64                     (*unmap_ip)(const struct map *, u64);
> > -
> >         struct dso              *dso;
> >         refcount_t              refcnt;
> > +       u32                     prot;
> >         u32                     flags;
> > +       enum mapping_type       mapping_type:8;
> > +       bool                    erange_warned;
> > +       bool                    priv;
> >  };
> >
> >  struct kmap;
> > @@ -41,38 +43,11 @@ struct kmap *__map__kmap(struct map *map);
> >  struct kmap *map__kmap(struct map *map);
> >  struct maps *map__kmaps(struct map *map);
> >
> > -/* ip -> dso rip */
> > -u64 map__dso_map_ip(const struct map *map, u64 ip);
> > -/* dso rip -> ip */
> > -u64 map__dso_unmap_ip(const struct map *map, u64 ip);
> > -/* Returns ip */
> > -u64 identity__map_ip(const struct map *map __maybe_unused, u64 ip);
> > -
> >  static inline struct dso *map__dso(const struct map *map)
> >  {
> >         return RC_CHK_ACCESS(map)->dso;
> >  }
> >
> > -static inline u64 map__map_ip(const struct map *map, u64 ip)
> > -{
> > -       return RC_CHK_ACCESS(map)->map_ip(map, ip);
> > -}
> > -
> > -static inline u64 map__unmap_ip(const struct map *map, u64 ip)
> > -{
> > -       return RC_CHK_ACCESS(map)->unmap_ip(map, ip);
> > -}
> > -
> > -static inline void *map__map_ip_ptr(struct map *map)
> > -{
> > -       return RC_CHK_ACCESS(map)->map_ip;
> > -}
> > -
> > -static inline void* map__unmap_ip_ptr(struct map *map)
> > -{
> > -       return RC_CHK_ACCESS(map)->unmap_ip;
> > -}
> > -
> >  static inline u64 map__start(const struct map *map)
> >  {
> >         return RC_CHK_ACCESS(map)->start;
> > @@ -123,6 +98,34 @@ static inline size_t map__size(const struct map *map)
> >         return map__end(map) - map__start(map);
> >  }
> >
> > +/* ip -> dso rip */
> > +static inline u64 map__dso_map_ip(const struct map *map, u64 ip)
> > +{
> > +       return ip - map__start(map) + map__pgoff(map);
> > +}
> > +
> > +/* dso rip -> ip */
> > +static inline u64 map__dso_unmap_ip(const struct map *map, u64 ip)
> 
> I think it's better to use 'rip' consistently in the variable name
> if possible.
> 
> Thanks,
> Namhyung
> 
> 
> > +{
> > +       return ip + map__start(map) - map__pgoff(map);
> > +}
> > +
> > +static inline u64 map__map_ip(const struct map *map, u64 ip)
> > +{
> > +       if ((RC_CHK_ACCESS(map)->mapping_type) == MAPPING_TYPE__DSO)
> > +               return map__dso_map_ip(map, ip);
> > +       else
> > +               return ip;
> > +}
> > +
> > +static inline u64 map__unmap_ip(const struct map *map, u64 ip)
> > +{
> > +       if ((RC_CHK_ACCESS(map)->mapping_type) == MAPPING_TYPE__DSO)
> > +               return map__dso_unmap_ip(map, ip);
> > +       else
> > +               return ip;
> > +}
> > +
> >  /* rip/ip <-> addr suitable for passing to `objdump --start-address=` */
> >  u64 map__rip_2objdump(struct map *map, u64 rip);
> >
> > @@ -294,13 +297,13 @@ static inline void map__set_dso(struct map *map, struct dso *dso)
> >         RC_CHK_ACCESS(map)->dso = dso;
> >  }
> >
> > -static inline void map__set_map_ip(struct map *map, u64 (*map_ip)(const struct map *map, u64 ip))
> > +static inline void map__set_mapping_type(struct map *map, enum mapping_type type)
> >  {
> > -       RC_CHK_ACCESS(map)->map_ip = map_ip;
> > +       RC_CHK_ACCESS(map)->mapping_type = type;
> >  }
> >
> > -static inline void map__set_unmap_ip(struct map *map, u64 (*unmap_ip)(const struct map *map, u64 rip))
> > +static inline enum mapping_type map__mapping_type(struct map *map)
> >  {
> > -       RC_CHK_ACCESS(map)->unmap_ip = unmap_ip;
> > +       return RC_CHK_ACCESS(map)->mapping_type;
> >  }
> >  #endif /* __PERF_MAP_H */
> > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> > index 9e7eeaf616b8..4b934ed3bfd1 100644
> > --- a/tools/perf/util/symbol-elf.c
> > +++ b/tools/perf/util/symbol-elf.c
> > @@ -1392,8 +1392,7 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
> >                         map__set_start(map, shdr->sh_addr + ref_reloc(kmap));
> >                         map__set_end(map, map__start(map) + shdr->sh_size);
> >                         map__set_pgoff(map, shdr->sh_offset);
> > -                       map__set_map_ip(map, map__dso_map_ip);
> > -                       map__set_unmap_ip(map, map__dso_unmap_ip);
> > +                       map__set_mapping_type(map, MAPPING_TYPE__DSO);
> >                         /* Ensure maps are correctly ordered */
> >                         if (kmaps) {
> >                                 int err;
> > @@ -1455,8 +1454,7 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
> >                         map__set_end(curr_map, map__start(curr_map) + shdr->sh_size);
> >                         map__set_pgoff(curr_map, shdr->sh_offset);
> >                 } else {
> > -                       map__set_map_ip(curr_map, identity__map_ip);
> > -                       map__set_unmap_ip(curr_map, identity__map_ip);
> > +                       map__set_mapping_type(curr_map, MAPPING_TYPE__IDENTITY);
> >                 }
> >                 curr_dso->symtab_type = dso->symtab_type;
> >                 if (maps__insert(kmaps, curr_map))
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index 82cc74b9358e..314c0263bf3c 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -956,8 +956,7 @@ static int maps__split_kallsyms(struct maps *kmaps, struct dso *dso, u64 delta,
> >                                 return -1;
> >                         }
> >
> > -                       map__set_map_ip(curr_map, identity__map_ip);
> > -                       map__set_unmap_ip(curr_map, identity__map_ip);
> > +                       map__set_mapping_type(curr_map, MAPPING_TYPE__IDENTITY);
> >                         if (maps__insert(kmaps, curr_map)) {
> >                                 dso__put(ndso);
> >                                 return -1;
> > @@ -1475,8 +1474,7 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> >                         map__set_start(map, map__start(new_map));
> >                         map__set_end(map, map__end(new_map));
> >                         map__set_pgoff(map, map__pgoff(new_map));
> > -                       map__set_map_ip(map, map__map_ip_ptr(new_map));
> > -                       map__set_unmap_ip(map, map__unmap_ip_ptr(new_map));
> > +                       map__set_mapping_type(map, map__mapping_type(new_map));
> >                         /* Ensure maps are correctly ordered */
> >                         map_ref = map__get(map);
> >                         maps__remove(kmaps, map_ref);
> > --
> > 2.43.0.rc1.413.gea7ed67945-goog
> >

-- 

- Arnaldo