From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f44.google.com (mail-ej1-f44.google.com [209.85.218.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7EC0E84A5A; Thu, 21 Mar 2024 14:57:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.44 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711033061; cv=none; b=L/fHaGI0uH4J3K7MZFHIK2ass6/GAlGDZEqSG+fudVGFRGyHpKjzwHgDk5yjifOXWGAFWchgPyrVjawkCU/X5ea4BTEirIb4TvoFqr5IvvdQXM6OzvNOo9Ki3D+yLFr2bAXAcIBuhHfmQZgjp1H2RUwEx1n/Br8Lqz583eg4frE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711033061; c=relaxed/simple; bh=OP5rImtzJo8ufuiNRhbyyhSsEnw8dl1VEzRpPhWVrTY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=mOikl5PJxRoqeRTTLEU8PVCGcDdOa2wLmA9EzNakwsDUKGJ6Vrn7mCQlnjOculhXXN+FJ3rJZhSPlUnz/HghfyeHcwWrOapE+qW3z5Sb9VQCs4o7PYI4UzVkNJJ/xpZLPYY+FB1QEpXQn5rowBWxPfzf/cCW8EhqmNs4mjZXcRc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=KWLffW4Y; arc=none smtp.client-ip=209.85.218.44 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KWLffW4Y" Received: by mail-ej1-f44.google.com with SMTP id a640c23a62f3a-a2f22bfb4e6so149327866b.0; Thu, 21 Mar 2024 07:57:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1711033057; x=1711637857; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=vPAsjljvq9spN9J6oarTkPbOp/uQy9Vt5YZP8TNCUI4=; b=KWLffW4Y0k8TAYZLhfd3ckpCmSf4dq6adWwlGES2BIvnsVHp/rP+Yrl+jEJvv0wgv/ s0zpqPbTTYlo8oWvmEHeUdNcDqDKfJ0E2xk1oKhrcISTK8O3MKCIneilfpvcWUxNnP8W fUUZ05aUWGehnbWVuKVbYgwZpzL/YzrIsehqYhAz447LFtQ9qNXgBg/O5bPqmWHdUUkI tgXMLs3Bf+IBZASrihwPp3bHpawhhqRcaRXbyEEItAqGBbb3xVIUPWGJsmNsiE0bbrCG aQOWO897OzhxL2JiKRcIiYasQhbaZFOYKELzscLWLLnSOlXPITNbKKjNjfpm+hNYANhk e7iw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1711033057; x=1711637857; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=vPAsjljvq9spN9J6oarTkPbOp/uQy9Vt5YZP8TNCUI4=; b=r7FA0CFQ5bzO9twkeUTwwHwwdMh8RpgyV0p8yjuCgVykQrAM9unuJtrIQD2tjGAf+I 9lWf2qCwCkzkwAcmeYWSseau2uTomTMBtEEdFpEtjJ8kEjEtlx695ZgSLufnSkEjnmwt tA2W7EBShXJa9pALZWUFGKNlkHVyDiQZF3QB1he6pw/5q+4mzJwt7tc2GCRdZ73Kr/Nd US57+iRJconO3WiroJMfQ8RR9q7gqrIrR15Kb+X46af4SalV2ianHbSMjGMdB6vpwigN ZdaSpdebInlSjvDzTRAyofsj+iP3VDNKjFooDOfktx2jpW1mk0PdrcNGKC8Q38hwgymS VFbg== X-Forwarded-Encrypted: i=1; AJvYcCWlsZM2+8foCDQf5msT5KgjwNdoTEVK6ZAJ7CIg35jvOwBcHMt0AD3ZE7y7FjxMEoqBevahE0sCemHG4p6Ht0X5uzuM/AbQR+F44KeLMPbFHhD0H38Qi2fE0BwHe5F5dIBIx8y6SilW9fcKcb6FwENiF5pTX0hkv6XwfsI8gSDRM77kYA== X-Gm-Message-State: AOJu0YxgwN3ZqXfd3D/zO5rKiqh1SGNciZ2xGYLN6QsIXSK6/07fK54w zs+cuc4Uls3iDN0IuT7Z/1Ew6ZfY4bKX6BNu9J8Aeij8u42J5Ae0l0i6+0ewbNGyEw== X-Google-Smtp-Source: AGHT+IFSqXkh2+8koR7VIEtj/qcJxmLHIngN30f6gr+BZ7rBiR3MmUYzBMVJ2N8B2BhwCtIBXUJa3w== X-Received: by 2002:a17:907:86a4:b0:a47:1d3f:b321 with SMTP id qa36-20020a17090786a400b00a471d3fb321mr650778ejc.8.1711033057333; Thu, 21 Mar 2024 07:57:37 -0700 (PDT) Received: from localhost (fwdproxy-lla-005.fbsv.net. [2a03:2880:30ff:5::face:b00c]) by smtp.gmail.com with ESMTPSA id bm19-20020a170906c05300b00a44180ab871sm5831ejb.50.2024.03.21.07.57.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Mar 2024 07:57:36 -0700 (PDT) From: Jonathan Haslam To: linux-trace-kernel@vger.kernel.org Cc: jonathan.haslam@gmail.com, andrii@kernel.org, bpf@vger.kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] uprobes: reduce contention on uprobes_tree access Date: Thu, 21 Mar 2024 07:57:35 -0700 Message-ID: <20240321145736.2373846-1-jonathan.haslam@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Active uprobes are stored in an RB tree and accesses to this tree are dominated by read operations. Currently these accesses are serialized by a spinlock but this leads to enormous contention when large numbers of threads are executing active probes. This patch converts the spinlock used to serialize access to the uprobes_tree RB tree into a reader-writer spinlock. This lock type aligns naturally with the overwhelmingly read-only nature of the tree usage here. Although the addition of reader-writer spinlocks are discouraged [0], this fix is proposed as an interim solution while an RCU based approach is implemented (that work is in a nascent form). This fix also has the benefit of being trivial, self contained and therefore simple to backport. This change has been tested against production workloads that exhibit significant contention on the spinlock and an almost order of magnitude reduction for mean uprobe execution time is observed (28 -> 3.5 microsecs). [0] https://docs.kernel.org/locking/spinlocks.html Signed-off-by: Jonathan Haslam --- kernel/events/uprobes.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 929e98c62965..42bf9b6e8bc0 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -39,7 +39,7 @@ static struct rb_root uprobes_tree = RB_ROOT; */ #define no_uprobe_events() RB_EMPTY_ROOT(&uprobes_tree) -static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */ +static DEFINE_RWLOCK(uprobes_treelock); /* serialize rbtree access */ #define UPROBES_HASH_SZ 13 /* serialize uprobe->pending_list */ @@ -669,9 +669,9 @@ static struct uprobe *find_uprobe(struct inode *inode, loff_t offset) { struct uprobe *uprobe; - spin_lock(&uprobes_treelock); + read_lock(&uprobes_treelock); uprobe = __find_uprobe(inode, offset); - spin_unlock(&uprobes_treelock); + read_unlock(&uprobes_treelock); return uprobe; } @@ -701,9 +701,9 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe) { struct uprobe *u; - spin_lock(&uprobes_treelock); + write_lock(&uprobes_treelock); u = __insert_uprobe(uprobe); - spin_unlock(&uprobes_treelock); + write_unlock(&uprobes_treelock); return u; } @@ -935,9 +935,9 @@ static void delete_uprobe(struct uprobe *uprobe) if (WARN_ON(!uprobe_is_active(uprobe))) return; - spin_lock(&uprobes_treelock); + write_lock(&uprobes_treelock); rb_erase(&uprobe->rb_node, &uprobes_tree); - spin_unlock(&uprobes_treelock); + write_unlock(&uprobes_treelock); RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */ put_uprobe(uprobe); } @@ -1298,7 +1298,7 @@ static void build_probe_list(struct inode *inode, min = vaddr_to_offset(vma, start); max = min + (end - start) - 1; - spin_lock(&uprobes_treelock); + read_lock(&uprobes_treelock); n = find_node_in_range(inode, min, max); if (n) { for (t = n; t; t = rb_prev(t)) { @@ -1316,7 +1316,7 @@ static void build_probe_list(struct inode *inode, get_uprobe(u); } } - spin_unlock(&uprobes_treelock); + read_unlock(&uprobes_treelock); } /* @vma contains reference counter, not the probed instruction. */ @@ -1407,9 +1407,9 @@ vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long e min = vaddr_to_offset(vma, start); max = min + (end - start) - 1; - spin_lock(&uprobes_treelock); + read_lock(&uprobes_treelock); n = find_node_in_range(inode, min, max); - spin_unlock(&uprobes_treelock); + read_unlock(&uprobes_treelock); return !!n; } -- 2.43.0