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bpf: Allow compiler to inline most of bpf_local_storage_lookup()
In various performance profiles of kernels with BPF programs attached, bpf_local_storage_lookup() appears as a significant portion of CPU cycles spent. To enable the compiler generate more optimal code, turn bpf_local_storage_lookup() into a static inline function, where only the cache insertion code path is outlined Notably, outlining cache insertion helps avoid bloating callers by duplicating setting up calls to raw_spin_{lock,unlock}_irqsave() (on architectures which do not inline spin_lock/unlock, such as x86), which would cause the compiler produce worse code by deciding to outline otherwise inlinable functions. The call overhead is neutral, because we make 2 calls either way: either calling raw_spin_lock_irqsave() and raw_spin_unlock_irqsave(); or call __bpf_local_storage_insert_cache(), which calls raw_spin_lock_irqsave(), followed by a tail-call to raw_spin_unlock_irqsave() where the compiler can perform TCO and (in optimized uninstrumented builds) turns it into a plain jump. The call to __bpf_local_storage_insert_cache() can be elided entirely if cacheit_lockit is a false constant expression. Based on results from './benchs/run_bench_local_storage.sh' (21 trials, reboot between each trial; x86 defconfig + BPF, clang 16) this produces improvements in throughput and latency in the majority of cases, with an average (geomean) improvement of 8%: +---- Hashmap Control -------------------- | | + num keys: 10 | : <before> | <after> | +-+ hashmap (control) sequential get +----------------------+---------------------- | +- hits throughput | 14.789 M ops/s | 14.745 M ops/s ( ~ ) | +- hits latency | 67.679 ns/op | 67.879 ns/op ( ~ ) | +- important_hits throughput | 14.789 M ops/s | 14.745 M ops/s ( ~ ) | | + num keys: 1000 | : <before> | <after> | +-+ hashmap (control) sequential get +----------------------+---------------------- | +- hits throughput | 12.233 M ops/s | 12.170 M ops/s ( ~ ) | +- hits latency | 81.754 ns/op | 82.185 ns/op ( ~ ) | +- important_hits throughput | 12.233 M ops/s | 12.170 M ops/s ( ~ ) | | + num keys: 10000 | : <before> | <after> | +-+ hashmap (control) sequential get +----------------------+---------------------- | +- hits throughput | 7.220 M ops/s | 7.204 M ops/s ( ~ ) | +- hits latency | 138.522 ns/op | 138.842 ns/op ( ~ ) | +- important_hits throughput | 7.220 M ops/s | 7.204 M ops/s ( ~ ) | | + num keys: 100000 | : <before> | <after> | +-+ hashmap (control) sequential get +----------------------+---------------------- | +- hits throughput | 5.061 M ops/s | 5.165 M ops/s (+2.1%) | +- hits latency | 198.483 ns/op | 194.270 ns/op (-2.1%) | +- important_hits throughput | 5.061 M ops/s | 5.165 M ops/s (+2.1%) | | + num keys: 4194304 | : <before> | <after> | +-+ hashmap (control) sequential get +----------------------+---------------------- | +- hits throughput | 2.864 M ops/s | 2.882 M ops/s ( ~ ) | +- hits latency | 365.220 ns/op | 361.418 ns/op (-1.0%) | +- important_hits throughput | 2.864 M ops/s | 2.882 M ops/s ( ~ ) | +---- Local Storage ---------------------- | | + num_maps: 1 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 33.005 M ops/s | 39.068 M ops/s (+18.4%) | +- hits latency | 30.300 ns/op | 25.598 ns/op (-15.5%) | +- important_hits throughput | 33.005 M ops/s | 39.068 M ops/s (+18.4%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 37.151 M ops/s | 44.926 M ops/s (+20.9%) | +- hits latency | 26.919 ns/op | 22.259 ns/op (-17.3%) | +- important_hits throughput | 37.151 M ops/s | 44.926 M ops/s (+20.9%) | | + num_maps: 10 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 32.288 M ops/s | 38.099 M ops/s (+18.0%) | +- hits latency | 30.972 ns/op | 26.248 ns/op (-15.3%) | +- important_hits throughput | 3.229 M ops/s | 3.810 M ops/s (+18.0%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 34.473 M ops/s | 41.145 M ops/s (+19.4%) | +- hits latency | 29.010 ns/op | 24.307 ns/op (-16.2%) | +- important_hits throughput | 12.312 M ops/s | 14.695 M ops/s (+19.4%) | | + num_maps: 16 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 32.524 M ops/s | 38.341 M ops/s (+17.9%) | +- hits latency | 30.748 ns/op | 26.083 ns/op (-15.2%) | +- important_hits throughput | 2.033 M ops/s | 2.396 M ops/s (+17.9%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 34.575 M ops/s | 41.338 M ops/s (+19.6%) | +- hits latency | 28.925 ns/op | 24.193 ns/op (-16.4%) | +- important_hits throughput | 11.001 M ops/s | 13.153 M ops/s (+19.6%) | | + num_maps: 17 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 28.861 M ops/s | 32.756 M ops/s (+13.5%) | +- hits latency | 34.649 ns/op | 30.530 ns/op (-11.9%) | +- important_hits throughput | 1.700 M ops/s | 1.929 M ops/s (+13.5%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 31.529 M ops/s | 36.110 M ops/s (+14.5%) | +- hits latency | 31.719 ns/op | 27.697 ns/op (-12.7%) | +- important_hits throughput | 9.598 M ops/s | 10.993 M ops/s (+14.5%) | | + num_maps: 24 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 18.602 M ops/s | 19.937 M ops/s (+7.2%) | +- hits latency | 53.767 ns/op | 50.166 ns/op (-6.7%) | +- important_hits throughput | 0.776 M ops/s | 0.831 M ops/s (+7.2%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 21.718 M ops/s | 23.332 M ops/s (+7.4%) | +- hits latency | 46.047 ns/op | 42.865 ns/op (-6.9%) | +- important_hits throughput | 6.110 M ops/s | 6.564 M ops/s (+7.4%) | | + num_maps: 32 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 14.118 M ops/s | 14.626 M ops/s (+3.6%) | +- hits latency | 70.856 ns/op | 68.381 ns/op (-3.5%) | +- important_hits throughput | 0.442 M ops/s | 0.458 M ops/s (+3.6%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 17.111 M ops/s | 17.906 M ops/s (+4.6%) | +- hits latency | 58.451 ns/op | 55.865 ns/op (-4.4%) | +- important_hits throughput | 4.776 M ops/s | 4.998 M ops/s (+4.6%) | | + num_maps: 100 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 5.281 M ops/s | 5.528 M ops/s (+4.7%) | +- hits latency | 192.398 ns/op | 183.059 ns/op (-4.9%) | +- important_hits throughput | 0.053 M ops/s | 0.055 M ops/s (+4.9%) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 6.265 M ops/s | 6.498 M ops/s (+3.7%) | +- hits latency | 161.436 ns/op | 152.877 ns/op (-5.3%) | +- important_hits throughput | 1.636 M ops/s | 1.697 M ops/s (+3.7%) | | + num_maps: 1000 | : <before> | <after> | +-+ local_storage cache sequential get +----------------------+---------------------- | +- hits throughput | 0.355 M ops/s | 0.354 M ops/s ( ~ ) | +- hits latency | 2826.538 ns/op | 2827.139 ns/op ( ~ ) | +- important_hits throughput | 0.000 M ops/s | 0.000 M ops/s ( ~ ) | : | : <before> | <after> | +-+ local_storage cache interleaved get +----------------------+---------------------- | +- hits throughput | 0.404 M ops/s | 0.403 M ops/s ( ~ ) | +- hits latency | 2481.190 ns/op | 2487.555 ns/op ( ~ ) | +- important_hits throughput | 0.102 M ops/s | 0.101 M ops/s ( ~ ) The on_lookup test in {cgrp,task}_ls_recursion.c is removed because the bpf_local_storage_lookup is no longer traceable and adding tracepoint will make the compiler generate worse code: https://lore.kernel.org/bpf/ZcJmok64Xqv6l4ZS@elver.google.com/ Signed-off-by: Marco Elver <elver@google.com> Cc: Martin KaFai Lau <martin.lau@linux.dev> Acked-by: Yonghong Song <yonghong.song@linux.dev> Link: https://lore.kernel.org/r/20240207122626.3508658-1-elver@google.com Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
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@ -129,10 +129,36 @@ bpf_local_storage_map_alloc(union bpf_attr *attr,
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struct bpf_local_storage_cache *cache,
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bool bpf_ma);
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struct bpf_local_storage_data *
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void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,
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struct bpf_local_storage_map *smap,
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struct bpf_local_storage_elem *selem);
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/* If cacheit_lockit is false, this lookup function is lockless */
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static inline struct bpf_local_storage_data *
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bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
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struct bpf_local_storage_map *smap,
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bool cacheit_lockit);
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bool cacheit_lockit)
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{
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struct bpf_local_storage_data *sdata;
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struct bpf_local_storage_elem *selem;
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/* Fast path (cache hit) */
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sdata = rcu_dereference_check(local_storage->cache[smap->cache_idx],
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bpf_rcu_lock_held());
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if (sdata && rcu_access_pointer(sdata->smap) == smap)
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return sdata;
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/* Slow path (cache miss) */
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hlist_for_each_entry_rcu(selem, &local_storage->list, snode,
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rcu_read_lock_trace_held())
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if (rcu_access_pointer(SDATA(selem)->smap) == smap)
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break;
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if (!selem)
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return NULL;
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if (cacheit_lockit)
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__bpf_local_storage_insert_cache(local_storage, smap, selem);
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return SDATA(selem);
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}
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void bpf_local_storage_destroy(struct bpf_local_storage *local_storage);
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@ -414,32 +414,10 @@ void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now)
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bpf_selem_unlink_storage(selem, reuse_now);
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}
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/* If cacheit_lockit is false, this lookup function is lockless */
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struct bpf_local_storage_data *
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bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
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void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,
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struct bpf_local_storage_map *smap,
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bool cacheit_lockit)
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struct bpf_local_storage_elem *selem)
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{
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struct bpf_local_storage_data *sdata;
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struct bpf_local_storage_elem *selem;
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/* Fast path (cache hit) */
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sdata = rcu_dereference_check(local_storage->cache[smap->cache_idx],
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bpf_rcu_lock_held());
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if (sdata && rcu_access_pointer(sdata->smap) == smap)
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return sdata;
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/* Slow path (cache miss) */
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hlist_for_each_entry_rcu(selem, &local_storage->list, snode,
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rcu_read_lock_trace_held())
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if (rcu_access_pointer(SDATA(selem)->smap) == smap)
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break;
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if (!selem)
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return NULL;
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sdata = SDATA(selem);
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if (cacheit_lockit) {
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unsigned long flags;
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/* spinlock is needed to avoid racing with the
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@ -449,14 +427,10 @@ bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
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*/
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raw_spin_lock_irqsave(&local_storage->lock, flags);
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if (selem_linked_to_storage(selem))
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rcu_assign_pointer(local_storage->cache[smap->cache_idx],
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sdata);
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rcu_assign_pointer(local_storage->cache[smap->cache_idx], SDATA(selem));
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raw_spin_unlock_irqrestore(&local_storage->lock, flags);
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}
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return sdata;
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}
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static int check_flags(const struct bpf_local_storage_data *old_sdata,
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u64 map_flags)
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{
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@ -117,12 +117,6 @@ static void test_recursion(void)
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ASSERT_OK(err, "lookup map_b");
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ASSERT_EQ(value, 100, "map_b value");
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prog_fd = bpf_program__fd(skel->progs.on_lookup);
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memset(&info, 0, sizeof(info));
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err = bpf_prog_get_info_by_fd(prog_fd, &info, &info_len);
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ASSERT_OK(err, "get prog info");
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ASSERT_GT(info.recursion_misses, 0, "on_lookup prog recursion");
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prog_fd = bpf_program__fd(skel->progs.on_update);
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memset(&info, 0, sizeof(info));
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err = bpf_prog_get_info_by_fd(prog_fd, &info, &info_len);
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@ -27,32 +27,6 @@ bool is_cgroup1 = 0;
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struct cgroup *bpf_task_get_cgroup1(struct task_struct *task, int hierarchy_id) __ksym;
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void bpf_cgroup_release(struct cgroup *cgrp) __ksym;
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static void __on_lookup(struct cgroup *cgrp)
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{
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bpf_cgrp_storage_delete(&map_a, cgrp);
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bpf_cgrp_storage_delete(&map_b, cgrp);
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}
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SEC("fentry/bpf_local_storage_lookup")
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int BPF_PROG(on_lookup)
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{
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struct task_struct *task = bpf_get_current_task_btf();
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struct cgroup *cgrp;
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if (is_cgroup1) {
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cgrp = bpf_task_get_cgroup1(task, target_hid);
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if (!cgrp)
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return 0;
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__on_lookup(cgrp);
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bpf_cgroup_release(cgrp);
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return 0;
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}
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__on_lookup(task->cgroups->dfl_cgrp);
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return 0;
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}
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static void __on_update(struct cgroup *cgrp)
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{
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long *ptr;
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@ -27,23 +27,6 @@ struct {
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__type(value, long);
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} map_b SEC(".maps");
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SEC("fentry/bpf_local_storage_lookup")
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int BPF_PROG(on_lookup)
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{
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struct task_struct *task = bpf_get_current_task_btf();
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if (!test_pid || task->pid != test_pid)
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return 0;
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/* The bpf_task_storage_delete will call
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* bpf_local_storage_lookup. The prog->active will
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* stop the recursion.
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*/
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bpf_task_storage_delete(&map_a, task);
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bpf_task_storage_delete(&map_b, task);
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return 0;
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}
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SEC("fentry/bpf_local_storage_update")
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int BPF_PROG(on_update)
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{
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