From: Martin KaFai Lau <kafai@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
David Miller <davem@davemloft.net>, <kernel-team@fb.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linux-Sparse <linux-sparse@vger.kernel.org>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
<netdev@vger.kernel.org>, Randy Dunlap <rdunlap@infradead.org>
Subject: [PATCH bpf] bpf: Improve bucket_log calculation logic
Date: Fri, 7 Feb 2020 00:18:10 -0800 [thread overview]
Message-ID: <20200207081810.3918919-1-kafai@fb.com> (raw)
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().
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>
---
net/core/bpf_sk_storage.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index 458be6b3eda9..3ab23f698221 100644
--- 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_map_alloc(union bpf_attr *attr)
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);
--
2.17.1
next reply other threads:[~2020-02-07 8:18 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-07 8:18 Martin KaFai Lau [this message]
2020-02-07 13:07 ` [PATCH bpf] bpf: Improve bucket_log calculation logic Luc Van Oostenryck
2020-02-07 18:07 ` Linus Torvalds
2020-02-07 19:39 ` Linus Torvalds
2020-02-07 20:41 ` Luc Van Oostenryck
2020-02-07 21:22 ` Linus Torvalds
2020-02-07 20:13 ` Alexei Starovoitov
2020-02-07 21:09 ` Linus Torvalds
2020-02-07 22:04 ` Daniel Borkmann
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