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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Martin KaFai Lau <kafai@fb.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Sasha Levin <sashal@kernel.org>,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: [PATCH AUTOSEL 5.4 117/459] bpf: Improve bucket_log calculation logic
Date: Fri, 14 Feb 2020 10:56:07 -0500
Message-ID: <20200214160149.11681-117-sashal@kernel.org> (raw)
In-Reply-To: <20200214160149.11681-1-sashal@kernel.org>

From: Martin KaFai Lau <kafai@fb.com>

[ Upstream commit 88d6f130e5632bbf419a2e184ec7adcbe241260b ]

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

  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: Sasha Levin <sashal@kernel.org>
 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 da5639a5bd3b9..0147b26f585a3 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);

  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200214160149.11681-1-sashal@kernel.org>
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 114/459] bpftool: Don't crash on missing xlated program instructions Sasha Levin
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 115/459] bpf, sockhash: Synchronize_rcu before free'ing map Sasha Levin
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 116/459] bpf, sockmap: Check update requirements after locking Sasha Levin
2020-02-14 15:56 ` Sasha Levin [this message]
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 118/459] bpf, sockmap: Don't sleep while holding RCU lock on tear-down Sasha Levin
2020-02-14 15:57 ` [PATCH AUTOSEL 5.4 186/459] samples/bpf: Set -fno-stack-protector when building BPF programs Sasha Levin
2020-02-14 15:57 ` [PATCH AUTOSEL 5.4 227/459] bpf: Print error message for bpftool cgroup show Sasha Levin
2020-02-14 15:58 ` [PATCH AUTOSEL 5.4 248/459] tools lib api fs: Fix gcc9 stringop-truncation compilation error Sasha Levin
2020-02-14 15:59 ` [PATCH AUTOSEL 5.4 307/459] bpf: Return -EBADRQC for invalid map type in __bpf_tx_xdp_map Sasha Levin
2020-02-14 16:00 ` [PATCH AUTOSEL 5.4 376/459] bpf, btf: Always output invariant hit in pahole DWARF to BTF transform Sasha Levin
2020-02-14 16:00 ` [PATCH AUTOSEL 5.4 397/459] selftests: bpf: Reset global state between reuseport test runs Sasha Levin
2020-02-14 16:01 ` [PATCH AUTOSEL 5.4 415/459] bpf: map_seq_next should always increase position index Sasha Levin
2020-02-14 16:01 ` [PATCH AUTOSEL 5.4 430/459] powerpc: Do not consider weak unresolved symbol relocations as bad Sasha Levin
2020-02-14 16:01 ` [PATCH AUTOSEL 5.4 455/459] i40e: Relax i40e_xsk_wakeup's return value when PF is busy Sasha Levin

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