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Date: Thu, 28 Feb 2019 12:08:17 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc: Andrii Nakryiko <andriin@...com>, Kernel Team <kernel-team@...com>,
Alexei Starovoitov <ast@...com>,
Networking <netdev@...r.kernel.org>, bpf@...r.kernel.org,
Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 3/5] btf: allow to customize dedup hash table size
On Thu, Feb 28, 2019 at 10:57 AM Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
>
> Em Wed, Feb 27, 2019 at 02:46:39PM -0800, Andrii Nakryiko escreveu:
> > Default size of dedup table (16k) is good enough for most binaries, even
> > typical vmlinux images. But there are cases of binaries with huge amount
> > of BTF types (e.g., allyesconfig variants of kernel), which benefit from
> > having bigger dedup table size to lower amount of unnecessary hash
> > collisions. Tools like pahole, thus, can tune this parameter to reach
> > optimal performance.
> >
> > This change also serves double purpose of allowing tests to force hash
> > collisions to test some corner cases, used in follow up patch.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> > tools/lib/bpf/btf.c | 43 ++++++++++++++++++++++++++-----------------
> > tools/lib/bpf/btf.h | 1 +
> > 2 files changed, 27 insertions(+), 17 deletions(-)
> >
> > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> > index 68b50e9bbde1..6bbb710216e6 100644
> > --- a/tools/lib/bpf/btf.c
> > +++ b/tools/lib/bpf/btf.c
> > @@ -1070,8 +1070,7 @@ int btf__dedup(struct btf *btf, struct btf_ext *btf_ext,
> > return err;
> > }
> >
> > -#define BTF_DEDUP_TABLE_SIZE_LOG 14
> > -#define BTF_DEDUP_TABLE_MOD ((1 << BTF_DEDUP_TABLE_SIZE_LOG) - 1)
> > +#define BTF_DEDUP_TABLE_DEFAULT_SIZE (1 << 14)
> > #define BTF_UNPROCESSED_ID ((__u32)-1)
> > #define BTF_IN_PROGRESS_ID ((__u32)-2)
> >
> > @@ -1128,18 +1127,21 @@ static inline __u32 hash_combine(__u32 h, __u32 value)
> > #undef GOLDEN_RATIO_PRIME
> > }
> >
> > -#define for_each_hash_node(table, hash, node) \
> > - for (node = table[hash & BTF_DEDUP_TABLE_MOD]; node; node = node->next)
> > +#define for_each_dedup_cand(d, hash, node) \
> > + for (node = d->dedup_table[hash & (d->opts.dedup_table_size - 1)]; \
> > + node; \
> > + node = node->next)
> >
> > static int btf_dedup_table_add(struct btf_dedup *d, __u32 hash, __u32 type_id)
> > {
> > struct btf_dedup_node *node = malloc(sizeof(struct btf_dedup_node));
> > + int bucket = hash & (d->opts.dedup_table_size - 1);
> >
> > if (!node)
> > return -ENOMEM;
> > node->type_id = type_id;
> > - node->next = d->dedup_table[hash & BTF_DEDUP_TABLE_MOD];
> > - d->dedup_table[hash & BTF_DEDUP_TABLE_MOD] = node;
> > + node->next = d->dedup_table[bucket];
> > + d->dedup_table[bucket] = node;
> > return 0;
> > }
> >
> > @@ -1177,7 +1179,7 @@ static void btf_dedup_table_free(struct btf_dedup *d)
> > if (!d->dedup_table)
> > return;
> >
> > - for (i = 0; i < (1 << BTF_DEDUP_TABLE_SIZE_LOG); i++) {
> > + for (i = 0; i < d->opts.dedup_table_size; i++) {
> > while (d->dedup_table[i]) {
> > tmp = d->dedup_table[i];
> > d->dedup_table[i] = tmp->next;
> > @@ -1221,10 +1223,19 @@ static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
> > if (!d)
> > return ERR_PTR(-ENOMEM);
> >
> > + d->opts.dont_resolve_fwds = opts && opts->dont_resolve_fwds;
>
> Is the above line a leftover from some other patch? Doesn't seem related
> to this patch.
>
> The rest seems ok.
No, I added another option and moved options processing to the top of
btf_dedup_new() (it used to be at the end, but it makes sense to first
process options, because they can be required during construction of
btf__dedup, as is the case for dedup_table_size).
>
> > + /* ensure table size is power of two and limit to 2G */
> > + d->opts.dedup_table_size = opts && opts->dedup_table_size
> > + ? opts->dedup_table_size
> > + : BTF_DEDUP_TABLE_DEFAULT_SIZE;
> > + for (i = 0; i < 31 && (1 << i) < d->opts.dedup_table_size; i++)
> > + ;
> > + d->opts.dedup_table_size = 1 << i;
> > +
> > d->btf = btf;
> > d->btf_ext = btf_ext;
> >
> > - d->dedup_table = calloc(1 << BTF_DEDUP_TABLE_SIZE_LOG,
> > + d->dedup_table = calloc(d->opts.dedup_table_size,
> > sizeof(struct btf_dedup_node *));
> > if (!d->dedup_table) {
> > err = -ENOMEM;
> > @@ -1249,8 +1260,6 @@ static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
> > for (i = 0; i <= btf->nr_types; i++)
> > d->hypot_map[i] = BTF_UNPROCESSED_ID;
> >
> > - d->opts.dont_resolve_fwds = opts && opts->dont_resolve_fwds;
> > -
> > done:
> > if (err) {
> > btf_dedup_free(d);
> > @@ -1824,7 +1833,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
> >
> > case BTF_KIND_INT:
> > h = btf_hash_int(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > cand = d->btf->types[cand_node->type_id];
> > if (btf_equal_int(t, cand)) {
> > new_id = cand_node->type_id;
> > @@ -1835,7 +1844,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
> >
> > case BTF_KIND_ENUM:
> > h = btf_hash_enum(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > cand = d->btf->types[cand_node->type_id];
> > if (btf_equal_enum(t, cand)) {
> > new_id = cand_node->type_id;
> > @@ -1846,7 +1855,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
> >
> > case BTF_KIND_FWD:
> > h = btf_hash_common(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > cand = d->btf->types[cand_node->type_id];
> > if (btf_equal_common(t, cand)) {
> > new_id = cand_node->type_id;
> > @@ -2263,7 +2272,7 @@ static int btf_dedup_struct_type(struct btf_dedup *d, __u32 type_id)
> > return 0;
> >
> > h = btf_hash_struct(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > int eq;
> >
> > btf_dedup_clear_hypot_map(d);
> > @@ -2349,7 +2358,7 @@ static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
> > t->type = ref_type_id;
> >
> > h = btf_hash_common(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > cand = d->btf->types[cand_node->type_id];
> > if (btf_equal_common(t, cand)) {
> > new_id = cand_node->type_id;
> > @@ -2372,7 +2381,7 @@ static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
> > info->index_type = ref_type_id;
> >
> > h = btf_hash_array(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > cand = d->btf->types[cand_node->type_id];
> > if (btf_equal_array(t, cand)) {
> > new_id = cand_node->type_id;
> > @@ -2403,7 +2412,7 @@ static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
> > }
> >
> > h = btf_hash_fnproto(t);
> > - for_each_hash_node(d->dedup_table, h, cand_node) {
> > + for_each_dedup_cand(d, h, cand_node) {
> > cand = d->btf->types[cand_node->type_id];
> > if (btf_equal_fnproto(t, cand)) {
> > new_id = cand_node->type_id;
> > diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> > index b60bb7cf5fff..28a1e1e59861 100644
> > --- a/tools/lib/bpf/btf.h
> > +++ b/tools/lib/bpf/btf.h
> > @@ -90,6 +90,7 @@ LIBBPF_API __u32 btf_ext__func_info_rec_size(const struct btf_ext *btf_ext);
> > LIBBPF_API __u32 btf_ext__line_info_rec_size(const struct btf_ext *btf_ext);
> >
> > struct btf_dedup_opts {
> > + unsigned int dedup_table_size;
> > bool dont_resolve_fwds;
> > };
> >
> > --
> > 2.17.1
>
> --
>
> - Arnaldo
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