From mboxrd@z Thu Jan 1 00:00:00 1970 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 2B05B18A6D7; Tue, 12 Nov 2024 00:28:21 +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=1731371302; cv=none; b=FDFXGE2rPDW7J5qoUR7/8tGOVj6KjAccBbekC5Gx2bqgl9ON3UddI1hkz+BQPq6MNnL2WSyF0lKbjNQBKgN/0RCpPnl7B302OtLaVjjHGMfn7T1IDZdFIicJAQclvb1ijjvCjwp9bJA1y14G0cUGNnNunzJQ/eQ/RET7AKN19oc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731371302; c=relaxed/simple; bh=Scn310P0r99vSey/hQL+jqRA1Hjarl50/MAqC1aF+n0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=lv7uNPMOCSXT+wRYPlEsaanmw3dMC6x0HspgtOVvZRD1Id/ETY0HjvUv1M9i8KJ3JUB61dvwbw0tY06aEnvxmfuomPVdj7gNgCvVAmq08mC/AwiZ/LsfiqBZfCquvf72vVTdANts1Jn/VmlSmXLcahWxHiHbOwey64XCfGlNrvs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mDYlTgXE; 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="mDYlTgXE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D5ADC4CECF; Tue, 12 Nov 2024 00:28:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731371301; bh=Scn310P0r99vSey/hQL+jqRA1Hjarl50/MAqC1aF+n0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=mDYlTgXEJ00ryIZ8Gso0ZK7CQ4cUZiPP6562rahLnqteePUD/g86rKCq/WfzYy+4R G27UCT8OZ2k+WfpgN4i+cOc1h3HMnj1OD2v3Trorde9mn96VFz3iveYkP8NPIOzXqU kD664bn0nULlPznsJ/MehYkRvFC4Tf+tDwVjfuEPqjm8RINIH75dj8uvbyThHKTXoc pcx/ZhEL1jJlaLHH4FSXPF+agBUs0azQcUVFw/pLGh6pJ63t13uALJFUk/eoSY+U1H 5WEHuEPxnvQbOYUWPhUTh4XdnQt9K4wD1yY6ynDjwCJsxdt6OUUXc+t4tUB870ujUZ IyH6RLmV4AFbA== Date: Tue, 12 Nov 2024 09:28:16 +0900 From: Masami Hiramatsu (Google) To: Andrii Nakryiko Cc: linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, peterz@infradead.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, shakeel.butt@linux.dev, hannes@cmpxchg.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, arnd@arndb.de, richard.weiyang@gmail.com, zhangpeng.00@bytedance.com, linmiaohe@huawei.com, viro@zeniv.linux.org.uk, hca@linux.ibm.com Subject: Re: [PATCH v4 tip/perf/core 4/4] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution Message-Id: <20241112092816.cf5b0aa1ef10f50ce872892f@kernel.org> In-Reply-To: <20241028010818.2487581-5-andrii@kernel.org> References: <20241028010818.2487581-1-andrii@kernel.org> <20241028010818.2487581-5-andrii@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Sun, 27 Oct 2024 18:08:18 -0700 Andrii Nakryiko wrote: > Given filp_cachep is marked SLAB_TYPESAFE_BY_RCU (and FMODE_BACKING > files, a special case, now goes through RCU-delated freeing), we can > safely access vma->vm_file->f_inode field locklessly under just > rcu_read_lock() protection, which enables looking up uprobe from > uprobes_tree completely locklessly and speculatively without the need to > acquire mmap_lock for reads. In most cases, anyway, assuming that there > are no parallel mm and/or VMA modifications. The underlying struct > file's memory won't go away from under us (even if struct file can be > reused in the meantime). > > We rely on newly added mmap_lock_speculation_{begin,end}() helpers to > validate that mm_struct stays intact for entire duration of this > speculation. If not, we fall back to mmap_lock-protected lookup. > The speculative logic is written in such a way that it will safely > handle any garbage values that might be read from vma or file structs. > > Benchmarking results speak for themselves. > > BEFORE (latest tip/perf/core) > ============================= > uprobe-nop ( 1 cpus): 3.384 ± 0.004M/s ( 3.384M/s/cpu) > uprobe-nop ( 2 cpus): 5.456 ± 0.005M/s ( 2.728M/s/cpu) > uprobe-nop ( 3 cpus): 7.863 ± 0.015M/s ( 2.621M/s/cpu) > uprobe-nop ( 4 cpus): 9.442 ± 0.008M/s ( 2.360M/s/cpu) > uprobe-nop ( 5 cpus): 11.036 ± 0.013M/s ( 2.207M/s/cpu) > uprobe-nop ( 6 cpus): 10.884 ± 0.019M/s ( 1.814M/s/cpu) > uprobe-nop ( 7 cpus): 7.897 ± 0.145M/s ( 1.128M/s/cpu) > uprobe-nop ( 8 cpus): 10.021 ± 0.128M/s ( 1.253M/s/cpu) > uprobe-nop (10 cpus): 9.932 ± 0.170M/s ( 0.993M/s/cpu) > uprobe-nop (12 cpus): 8.369 ± 0.056M/s ( 0.697M/s/cpu) > uprobe-nop (14 cpus): 8.678 ± 0.017M/s ( 0.620M/s/cpu) > uprobe-nop (16 cpus): 7.392 ± 0.003M/s ( 0.462M/s/cpu) > uprobe-nop (24 cpus): 5.326 ± 0.178M/s ( 0.222M/s/cpu) > uprobe-nop (32 cpus): 5.426 ± 0.059M/s ( 0.170M/s/cpu) > uprobe-nop (40 cpus): 5.262 ± 0.070M/s ( 0.132M/s/cpu) > uprobe-nop (48 cpus): 6.121 ± 0.010M/s ( 0.128M/s/cpu) > uprobe-nop (56 cpus): 6.252 ± 0.035M/s ( 0.112M/s/cpu) > uprobe-nop (64 cpus): 7.644 ± 0.023M/s ( 0.119M/s/cpu) > uprobe-nop (72 cpus): 7.781 ± 0.001M/s ( 0.108M/s/cpu) > uprobe-nop (80 cpus): 8.992 ± 0.048M/s ( 0.112M/s/cpu) > > AFTER > ===== > uprobe-nop ( 1 cpus): 3.534 ± 0.033M/s ( 3.534M/s/cpu) > uprobe-nop ( 2 cpus): 6.701 ± 0.007M/s ( 3.351M/s/cpu) > uprobe-nop ( 3 cpus): 10.031 ± 0.007M/s ( 3.344M/s/cpu) > uprobe-nop ( 4 cpus): 13.003 ± 0.012M/s ( 3.251M/s/cpu) > uprobe-nop ( 5 cpus): 16.274 ± 0.006M/s ( 3.255M/s/cpu) > uprobe-nop ( 6 cpus): 19.563 ± 0.024M/s ( 3.261M/s/cpu) > uprobe-nop ( 7 cpus): 22.696 ± 0.054M/s ( 3.242M/s/cpu) > uprobe-nop ( 8 cpus): 24.534 ± 0.010M/s ( 3.067M/s/cpu) > uprobe-nop (10 cpus): 30.475 ± 0.117M/s ( 3.047M/s/cpu) > uprobe-nop (12 cpus): 33.371 ± 0.017M/s ( 2.781M/s/cpu) > uprobe-nop (14 cpus): 38.864 ± 0.004M/s ( 2.776M/s/cpu) > uprobe-nop (16 cpus): 41.476 ± 0.020M/s ( 2.592M/s/cpu) > uprobe-nop (24 cpus): 64.696 ± 0.021M/s ( 2.696M/s/cpu) > uprobe-nop (32 cpus): 85.054 ± 0.027M/s ( 2.658M/s/cpu) > uprobe-nop (40 cpus): 101.979 ± 0.032M/s ( 2.549M/s/cpu) > uprobe-nop (48 cpus): 110.518 ± 0.056M/s ( 2.302M/s/cpu) > uprobe-nop (56 cpus): 117.737 ± 0.020M/s ( 2.102M/s/cpu) > uprobe-nop (64 cpus): 124.613 ± 0.079M/s ( 1.947M/s/cpu) > uprobe-nop (72 cpus): 133.239 ± 0.032M/s ( 1.851M/s/cpu) > uprobe-nop (80 cpus): 142.037 ± 0.138M/s ( 1.775M/s/cpu) > > Previously total throughput was maxing out at 11mln/s, and gradually > declining past 8 cores. With this change, it now keeps growing with each > added CPU, reaching 142mln/s at 80 CPUs (this was measured on a 80-core > Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz). > Looks good to me, except one question below. > Reviewed-by: Oleg Nesterov > Suggested-by: Matthew Wilcox > Suggested-by: Peter Zijlstra > Signed-off-by: Andrii Nakryiko > --- > kernel/events/uprobes.c | 45 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 45 insertions(+) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 290c445768fa..efcd62f7051d 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -2074,6 +2074,47 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > return is_trap_insn(&opcode); > } > > +static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > +{ > + struct mm_struct *mm = current->mm; > + struct uprobe *uprobe = NULL; > + struct vm_area_struct *vma; > + struct file *vm_file; > + loff_t offset; > + unsigned int seq; > + > + guard(rcu)(); > + > + if (!mmap_lock_speculation_begin(mm, &seq)) > + return NULL; > + > + vma = vma_lookup(mm, bp_vaddr); > + if (!vma) > + return NULL; > + > + /* > + * vm_file memory can be reused for another instance of struct file, > + * but can't be freed from under us, so it's safe to read fields from > + * it, even if the values are some garbage values; ultimately > + * find_uprobe_rcu() + mmap_lock_speculation_end() check will ensure > + * that whatever we speculatively found is correct If vm_file is a garbage value, may `vm_file->f_inode` access be dangerous? > + */ > + vm_file = READ_ONCE(vma->vm_file); > + if (!vm_file) > + return NULL; > + > + offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start); > + uprobe = find_uprobe_rcu(vm_file->f_inode, offset); ^^^^ Here if it only stores vm_file or NULL, there's no problem. Thank you, > + if (!uprobe) > + return NULL; > + > + /* now double check that nothing about MM changed */ > + if (!mmap_lock_speculation_end(mm, seq)) > + return NULL; > + > + return uprobe; > +} > + > /* assumes being inside RCU protected region */ > static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swbp) > { > @@ -2081,6 +2122,10 @@ static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swb > struct uprobe *uprobe = NULL; > struct vm_area_struct *vma; > > + uprobe = find_active_uprobe_speculative(bp_vaddr); > + if (uprobe) > + return uprobe; > + > mmap_read_lock(mm); > vma = vma_lookup(mm, bp_vaddr); > if (vma) { > -- > 2.43.5 > -- Masami Hiramatsu (Google)