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 690C24C99; Sat, 30 Mar 2024 00:36:37 +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=1711758997; cv=none; b=aJYnkLMP/hx8h5cXw1agNxu/TXM/A8GFGi2/Da6/0ow8ugVlA9NpvIlMKNAV++NydOfztyNwLnLATjITXsypoMHts7lgseKJ3Htj73pKRaDxN/iRGZ/SZ/yYBtjZVICRVMRkRIJ4dhTzcCldFWNRpJ7Gm5N8tCW1ZN9s6II3m4Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711758997; c=relaxed/simple; bh=Ab+AY7ZyWjpeu6FnqcS57xd1DicB744MIAHuv5agtGA=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=NYteGYA59tTgIWKVD1/2AoveuwbTibp1YB2WlGNq0RS5l60/IpFr5b7uDpKb3WKWHH9Z4QUfy2NLMpRwoFyo90IN9xOOGDhgnptoes3FWzQJPDZU+sicPCK899eAtIrXf3Cobwdpi2tFPMT6DTLQVRWoSvOXpzvkXApkGO6pAE4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AZXHiFll; 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="AZXHiFll" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 392F4C433C7; Sat, 30 Mar 2024 00:36:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711758996; bh=Ab+AY7ZyWjpeu6FnqcS57xd1DicB744MIAHuv5agtGA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=AZXHiFllv8n5dEaSG9m4+IXHeGilu8MA8ZUo6p+KaOcte1zmtfBf+jY8/nBvOgW/I ai1q2UJHlVf956ZvihVKGnslmGGvU3irYFpvNniaPIKZQsFffeIse4JwIsUUBMRETt 0P1IYSAQi0EHzxbRsTY5HrURviRvdA2Qa1TK2nNsGxcpB/gDvJMAmakNAX1WvtzdrN 2dEGvyeZTeNi2FwfB0tSqbmYKcexm69MPa9h9sl70npMH+TAvsctqxdmKkMIlSVkNz 1vdFb1WSJyFTEDdJSrkuQsPR0JimgzdoclZ9Mh5/uG1SQvXl/GKJFW+mxSv4G9LYX+ dtZkOsjeRbWnA== Date: Sat, 30 Mar 2024 09:36:31 +0900 From: Masami Hiramatsu (Google) To: Andrii Nakryiko Cc: Jonthan Haslam , linux-trace-kernel@vger.kernel.org, andrii@kernel.org, bpf@vger.kernel.org, rostedt@goodmis.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: Re: [PATCH] uprobes: reduce contention on uprobes_tree access Message-Id: <20240330093631.72273967ba818cb16aeb58b6@kernel.org> In-Reply-To: References: <20240321145736.2373846-1-jonathan.haslam@gmail.com> <20240325120323.ec3248d330b2755e73a6571e@kernel.org> <20240327084245.a890ae12e579f0be1902ae4a@kernel.org> <54jakntmdyedadce7yrf6kljcjapbwyoqqt26dnllrqvs3pg7x@itra4a2ikgqw> <20240328091841.ce9cc613db375536de843cfb@kernel.org> X-Mailer: Sylpheed 3.7.0 (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 Fri, 29 Mar 2024 10:33:57 -0700 Andrii Nakryiko wrote: > On Wed, Mar 27, 2024 at 5:45 PM Andrii Nakryiko > wrote: > > > > On Wed, Mar 27, 2024 at 5:18 PM Masami Hiramatsu wrote: > > > > > > On Wed, 27 Mar 2024 17:06:01 +0000 > > > Jonthan Haslam wrote: > > > > > > > > > Masami, > > > > > > > > > > > > Given the discussion around per-cpu rw semaphore and need for > > > > > > (internal) batched attachment API for uprobes, do you think you can > > > > > > apply this patch as is for now? We can then gain initial improvements > > > > > > in scalability that are also easy to backport, and Jonathan will work > > > > > > on a more complete solution based on per-cpu RW semaphore, as > > > > > > suggested by Ingo. > > > > > > > > > > Yeah, it is interesting to use per-cpu rw semaphore on uprobe. > > > > > I would like to wait for the next version. > > > > > > > > My initial tests show a nice improvement on the over RW spinlocks but > > > > significant regression in acquiring a write lock. I've got a few days > > > > vacation over Easter but I'll aim to get some more formalised results out > > > > to the thread toward the end of next week. > > > > > > As far as the write lock is only on the cold path, I think you can choose > > > per-cpu RW semaphore. Since it does not do busy wait, the total system > > > performance impact will be small. > > > > No, Masami, unfortunately it's not as simple. In BPF we have BPF > > multi-uprobe, which can be used to attach to thousands of user > > functions. It currently creates one uprobe at a time, as we don't > > really have a batched API. If each such uprobe registration will now > > take a (relatively) long time, when multiplied by number of attach-to > > user functions, it will be a horrible regression in terms of > > attachment/detachment performance. Ah, got it. So attachment/detachment performance should be counted. > > > > So when we switch to per-CPU rw semaphore, we'll need to provide an > > internal batch uprobe attach/detach API to make sure that attaching to > > multiple uprobes is still fast. Yeah, we need such interface like register_uprobes(...). > > > > Which is why I was asking to land this patch as is, as it relieves the > > scalability pains in production and is easy to backport to old > > kernels. And then we can work on batched APIs and switch to per-CPU rw > > semaphore. OK, then I'll push this to for-next at this moment. Please share if you have a good idea for the batch interface which can be backported. I guess it should involve updating userspace changes too. Thank you! > > > > So I hope you can reconsider and accept improvements in this patch, > > while Jonathan will keep working on even better final solution. > > Thanks! > > > > > I look forward to your formalized results :) > > > > > BTW, as part of BPF selftests, we have a multi-attach test for uprobes > and USDTs, reporting attach/detach timings: > $ sudo ./test_progs -v -t uprobe_multi_test/bench > bpf_testmod.ko is already unloaded. > Loading bpf_testmod.ko... > Successfully loaded bpf_testmod.ko. > test_bench_attach_uprobe:PASS:uprobe_multi_bench__open_and_load 0 nsec > test_bench_attach_uprobe:PASS:uprobe_multi_bench__attach 0 nsec > test_bench_attach_uprobe:PASS:uprobes_count 0 nsec > test_bench_attach_uprobe: attached in 0.120s > test_bench_attach_uprobe: detached in 0.092s > #400/5 uprobe_multi_test/bench_uprobe:OK > test_bench_attach_usdt:PASS:uprobe_multi__open 0 nsec > test_bench_attach_usdt:PASS:bpf_program__attach_usdt 0 nsec > test_bench_attach_usdt:PASS:usdt_count 0 nsec > test_bench_attach_usdt: attached in 0.124s > test_bench_attach_usdt: detached in 0.064s > #400/6 uprobe_multi_test/bench_usdt:OK > #400 uprobe_multi_test:OK > Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED > Successfully unloaded bpf_testmod.ko. > > So it should be easy for Jonathan to validate his changes with this. > > > > Thank you, > > > > > > > > > > > Jon. > > > > > > > > > > > > > > Thank you, > > > > > > > > > > > > > > > > > > > > > > > > > BTW, how did you measure the overhead? I think spinlock overhead > > > > > > > will depend on how much lock contention happens. > > > > > > > > > > > > > > Thank you, > > > > > > > > > > > > > > > > > > > > > > > [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 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > Masami Hiramatsu (Google) > > > > > > > > > > > > > > > -- > > > > > Masami Hiramatsu (Google) > > > > > > > > > -- > > > Masami Hiramatsu (Google) -- Masami Hiramatsu (Google)