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

From: Namhyung Kim
Date: Mon Dec 04 2023 - 18:39:35 EST

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Hi Ian,

On Mon, Nov 27, 2023 at 2:09 PM Ian Rogers <irogers@xxxxxxxxxx> 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@xxxxxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

A few nitpicks below.

> ---
> 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
>

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