| From 88d6f130e5632bbf419a2e184ec7adcbe241260b Mon Sep 17 00:00:00 2001 |
| From: Martin KaFai Lau <kafai@fb.com> |
| Date: Fri, 7 Feb 2020 00:18:10 -0800 |
| Subject: bpf: Improve bucket_log calculation logic |
| |
| From: Martin KaFai Lau <kafai@fb.com> |
| |
| commit 88d6f130e5632bbf419a2e184ec7adcbe241260b upstream. |
| |
| It was reported that the max_t, ilog2, and roundup_pow_of_two macros have |
| exponential effects on the number of states in the sparse checker. |
| |
| This patch breaks them up by calculating the "nbuckets" first so that the |
| "bucket_log" only needs to take ilog2(). |
| |
| In addition, Linus mentioned: |
| |
| Patch looks good, but I'd like to point out that it's not just sparse. |
| |
| You can see it with a simple |
| |
| make net/core/bpf_sk_storage.i |
| grep 'smap->bucket_log = ' net/core/bpf_sk_storage.i | wc |
| |
| and see the end result: |
| |
| 1 365071 2686974 |
| |
| That's one line (the assignment line) that is 2,686,974 characters in |
| length. |
| |
| Now, sparse does happen to react particularly badly to that (I didn't |
| look to why, but I suspect it's just that evaluating all the types |
| that don't actually ever end up getting used ends up being much more |
| expensive than it should be), but I bet it's not good for gcc either. |
| |
| Fixes: 6ac99e8f23d4 ("bpf: Introduce bpf sk local storage") |
| Reported-by: Randy Dunlap <rdunlap@infradead.org> |
| Reported-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> |
| Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Martin KaFai Lau <kafai@fb.com> |
| Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> |
| Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> |
| Link: https://lore.kernel.org/bpf/20200207081810.3918919-1-kafai@fb.com |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| net/core/bpf_sk_storage.c | 5 +++-- |
| 1 file changed, 3 insertions(+), 2 deletions(-) |
| |
| --- a/net/core/bpf_sk_storage.c |
| +++ b/net/core/bpf_sk_storage.c |
| @@ -643,9 +643,10 @@ static struct bpf_map *bpf_sk_storage_ma |
| return ERR_PTR(-ENOMEM); |
| bpf_map_init_from_attr(&smap->map, attr); |
| |
| + nbuckets = roundup_pow_of_two(num_possible_cpus()); |
| /* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */ |
| - smap->bucket_log = max_t(u32, 1, ilog2(roundup_pow_of_two(num_possible_cpus()))); |
| - nbuckets = 1U << smap->bucket_log; |
| + nbuckets = max_t(u32, 2, nbuckets); |
| + smap->bucket_log = ilog2(nbuckets); |
| cost = sizeof(*smap->buckets) * nbuckets + sizeof(*smap); |
| |
| ret = bpf_map_charge_init(&smap->map.memory, cost); |