From patchwork Mon Mar 18 13:25:26 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jesper Dangaard Brouer X-Patchwork-Id: 13595368 X-Patchwork-Delegate: bpf@iogearbox.net Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8DF1647F4B; Mon, 18 Mar 2024 13:25:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710768331; cv=none; b=mBoAEwrTT5G2tE+437yrrj2lsOBrwyWAyODdJeJ69iJqmjIg/a/ngBzn9C8/tElCYtiloSfvuXInIM3+cu5Yr8eXQ91WbTt8WraMdIsfs8lDLa7o4E4X3n10L2zFeM/A1Iqt8jwmgT3wrpaWOPvE5PDmgWEB9fyoT6keJhEEmow= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710768331; c=relaxed/simple; bh=Vf12dd/Egl8nCL4fAZyQY6z00cZn1KGW7EOXwQXKS2U=; h=Subject:From:To:Cc:Date:Message-ID:MIME-Version:Content-Type; b=jYDRk23uCmrKRNVxbz6WkyQE/UzSkCWPfjW3TWC8HafOJrLRTg+rTrrJOsebflaef9SuxrNb5ki9r1RqyDdCssNCBtqvaPUjdFQTP5SFJh3hiE3pwiZuBzuK088yL+2UaEU4bTF/zaCL/fMwEgOoeXtcBIgq6SAZalj2Zht6HeM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GYhEnCDy; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GYhEnCDy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D813C433F1; Mon, 18 Mar 2024 13:25:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710768331; bh=Vf12dd/Egl8nCL4fAZyQY6z00cZn1KGW7EOXwQXKS2U=; h=Subject:From:To:Cc:Date:From; b=GYhEnCDyMs3UBDxenTSxg/j7DlqzZZigVWDEAdzKdsoknZd1yF0TQ6zmbbp+7u9Gl /BaCU6v7ke+D/B8cEFv7C3jthtvuWjrFAhWsq9eBCwasJu5TRcv4sdvrbmST7qz95T 8Tjfdb5pJcuhstJ9XMQDSv/2gDY03HKQcD141p5xrtHfqiL3ug76gAwBKg88li66nn C3mOE0qz4EawfX8nuqngaeLicL6gUoLfksRHeb4KU2vthZa/JQMpW56HuC1OMU0T6Z 94Dt+n9Of2bzWd2zolh1lBpjoIJKgD4cvqPCFg9+l/ZvgFOHtAizuKaSjex6MSm66f YKBXntQY336NQ== Subject: [PATCH bpf-next V2] bpf/lpm_trie: inline longest_prefix_match for fastpath From: Jesper Dangaard Brouer To: bpf@vger.kernel.org, Daniel Borkmann Cc: Jesper Dangaard Brouer , Alexei Starovoitov , martin.lau@kernel.org, netdev@vger.kernel.org, bp@alien8.de, kernel-team@cloudflare.com Date: Mon, 18 Mar 2024 14:25:26 +0100 Message-ID: <171076828575.2141737.18370644069389889027.stgit@firesoul> User-Agent: StGit/1.5 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net The BPF map type LPM (Longest Prefix Match) is used heavily in production by multiple products that have BPF components. Perf data shows trie_lookup_elem() and longest_prefix_match() being part of kernels perf top. For every level in the LPM tree trie_lookup_elem() calls out to longest_prefix_match(). The compiler is free to inline this call, but chooses not to inline, because other slowpath callers (that can be invoked via syscall) exists like trie_update_elem(), trie_delete_elem() or trie_get_next_key(). bcc/tools/funccount -Ti 1 'trie_lookup_elem|longest_prefix_match.isra.0' FUNC COUNT trie_lookup_elem 664945 longest_prefix_match.isra.0 8101507 Observation on a single random machine shows a factor 12 between the two functions. Given an average of 12 levels in the trie being searched. This patch force inlining longest_prefix_match(), but only for the lookup fastpath to balance object instruction size. In production with AMD CPUs, measuring the function latency of 'trie_lookup_elem' (bcc/tools/funclatency) we are seeing an improvement function latency reduction 7-8% with this patch applied (to production kernels 6.6 and 6.1). Analyzing perf data, we can explain this rather large improvement due to reducing the overhead for AMD side-channel mitigation SRSO (Speculative Return Stack Overflow). Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation") Signed-off-by: Jesper Dangaard Brouer Acked-by: Yonghong Song --- kernel/bpf/lpm_trie.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index 050fe1ebf0f7..939620b91c0e 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -155,16 +155,17 @@ static inline int extract_bit(const u8 *data, size_t index) } /** - * longest_prefix_match() - determine the longest prefix + * __longest_prefix_match() - determine the longest prefix * @trie: The trie to get internal sizes from * @node: The node to operate on * @key: The key to compare to @node * * Determine the longest prefix of @node that matches the bits in @key. */ -static size_t longest_prefix_match(const struct lpm_trie *trie, - const struct lpm_trie_node *node, - const struct bpf_lpm_trie_key_u8 *key) +static __always_inline +size_t __longest_prefix_match(const struct lpm_trie *trie, + const struct lpm_trie_node *node, + const struct bpf_lpm_trie_key_u8 *key) { u32 limit = min(node->prefixlen, key->prefixlen); u32 prefixlen = 0, i = 0; @@ -224,6 +225,13 @@ static size_t longest_prefix_match(const struct lpm_trie *trie, return prefixlen; } +static size_t longest_prefix_match(const struct lpm_trie *trie, + const struct lpm_trie_node *node, + const struct bpf_lpm_trie_key_u8 *key) +{ + return __longest_prefix_match(trie, node, key); +} + /* Called from syscall or from eBPF program */ static void *trie_lookup_elem(struct bpf_map *map, void *_key) { @@ -245,7 +253,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key) * If it's the maximum possible prefix for this trie, we have * an exact match and can return it directly. */ - matchlen = longest_prefix_match(trie, node, key); + matchlen = __longest_prefix_match(trie, node, key); if (matchlen == trie->max_prefixlen) { found = node; break;