From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 8968C34F25E; Tue, 21 Oct 2025 17:19:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761067151; cv=none; b=GEt707LA3PjJgAygTi0n82FuTgehiIeEad6yYBFUKCYnsPcpHx72LMPMy7VTz2KyofzmuAEHupZq8ofqIrkrMkDdMXRryCsinvXQnpPDquK5o97HQ/nbmeFozQMq2jE5DM3vgV9/V3apUnBroJszJP8ziLhgg7/tSD2pDLaKi6Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761067151; c=relaxed/simple; bh=QsHFvi//g4HRcWfugd+JY1chiMBqOhI9UXQyr1+ljSs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NZHPZsBJDtb3fVU229n2x3qBTfm8d7vsCT+RTtG55dKJ7PSxX09SwtEigO31E4VhUD7mZKMlJN2ROOGrzYpL/lqyTDv6kfMHavGIZ9y4ny1XNRnXHodp8wE9n/1LPkzrR3576TQnUJQV2ZwKmbwQFM2SEyD5CabY5i8MAfAWxBw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=LB9bd8MD; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="LB9bd8MD" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=RSjTgo/UGZZgGAoRYbVD0IljFiwy3i9IhIYBJ8qHaDM=; b=LB9bd8MDfmb03oYRhY77QkhDtG f+DqEN5CUg6EZW9udx1ma8UHKwqLH/FP4meJrfBKiilWzdAuTrg8DqqzsC6Kcg7xja0JZmAi0WwIE P1wl25DaZJ4fUgiC4cUoaxS7gtqAjvAQCagWPmqeVgBACRQR4hvf9TxrguTCQZbYcQGjxJ1LbCjuA vyJ706fFka2qoCsPObKQ1MMffgoYfccGV9H6wHVOyek6eWlZthIMlp3e4zA3x6VABved+oN2YXMd4 vT9DOobxQH5tpdBrxzLk1xTkFWN7rWEycLRJeXwoI0l2cQM9zOfTLgxX438j5jA2DcBXMoSS94J48 PxLVA66Q==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vBG0f-0000000DsZX-012g; Tue, 21 Oct 2025 17:18:58 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 39E093030D8; Mon, 20 Oct 2025 13:40:40 +0200 (CEST) Date: Mon, 20 Oct 2025 13:40:40 +0200 From: Peter Zijlstra To: Tao Chen Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, song@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH bpf-next v3 1/2] perf: Use extern perf_callchain_entry for get_perf_callchain Message-ID: <20251020114040.GT3419281@noisy.programming.kicks-ass.net> References: <20251019170118.2955346-1-chen.dylane@linux.dev> <20251019170118.2955346-2-chen.dylane@linux.dev> 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=us-ascii Content-Disposition: inline In-Reply-To: <20251019170118.2955346-2-chen.dylane@linux.dev> On Mon, Oct 20, 2025 at 01:01:17AM +0800, Tao Chen wrote: > From bpf stack map, we want to use our own buffers to avoid unnecessary > copy, so let us pass it directly. BPF will use this in the next patch. > > Signed-off-by: Tao Chen > --- > diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c > index 808c0d7a31f..851e8f9d026 100644 > --- a/kernel/events/callchain.c > +++ b/kernel/events/callchain.c > @@ -217,8 +217,8 @@ static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entr > } > > struct perf_callchain_entry * > -get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, > - u32 max_stack, bool crosstask, bool add_mark) > +get_perf_callchain(struct pt_regs *regs, struct perf_callchain_entry *external_entry, > + bool kernel, bool user, u32 max_stack, bool crosstask, bool add_mark) > { > struct perf_callchain_entry *entry; > struct perf_callchain_entry_ctx ctx; > @@ -228,7 +228,11 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, > if (crosstask && user && !kernel) > return NULL; > > - entry = get_callchain_entry(&rctx); > + if (external_entry) > + entry = external_entry; > + else > + entry = get_callchain_entry(&rctx); > + > if (!entry) > return NULL; > > @@ -260,7 +264,8 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, > } > > exit_put: > - put_callchain_entry(rctx); > + if (!external_entry) > + put_callchain_entry(rctx); > > return entry; > } Urgh.. How about something like the below, and then you fix up __bpf_get_stack() a little like this: diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 4d53cdd1374c..8b85b49cecf7 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -303,8 +303,8 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, u32 max_depth = map->value_size / stack_map_data_size(map); u32 skip = flags & BPF_F_SKIP_FIELD_MASK; bool user = flags & BPF_F_USER_STACK; + struct perf_callchain_entry_ctx ctx; struct perf_callchain_entry *trace; - bool kernel = !user; if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) @@ -314,8 +314,13 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, if (max_depth > sysctl_perf_event_max_stack) max_depth = sysctl_perf_event_max_stack; - trace = get_perf_callchain(regs, kernel, user, max_depth, - false, false); + trace = your-stuff; + + __init_perf_callchain_ctx(&ctx, trace, max_depth, false); + if (!user) + __get_perf_callchain_kernel(&ctx, regs); + else + __get_perf_callchain_user(&ctx, regs); if (unlikely(!trace)) /* couldn't fetch the stack trace */ --- diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index fd1d91017b99..14a382cad1dd 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -67,6 +67,7 @@ struct perf_callchain_entry_ctx { u32 nr; short contexts; bool contexts_maxed; + bool add_mark; }; typedef unsigned long (*perf_copy_f)(void *dst, const void *src, @@ -1718,9 +1719,17 @@ DECLARE_PER_CPU(struct perf_callchain_entry, perf_callchain_entry); extern void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs); extern void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs); + +extern void __init_perf_callchain_ctx(struct perf_callchain_entry_ctx *ctx, + struct perf_callchain_entry *entry, + u32 max_stack, bool add_mark); + +extern void __get_perf_callchain_kernel(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs); +extern void __get_perf_callchain_user(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs); + extern struct perf_callchain_entry * get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, - u32 max_stack, bool crosstask, bool add_mark); + u32 max_stack, bool crosstask); extern int get_callchain_buffers(int max_stack); extern void put_callchain_buffers(void); extern struct perf_callchain_entry *get_callchain_entry(int *rctx); diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index 808c0d7a31fa..edd76e3bb139 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -216,50 +216,70 @@ static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entr #endif } +void __init_perf_callchain_ctx(struct perf_callchain_entry_ctx *ctx, + struct perf_callchain_entry *entry, + u32 max_stack, bool add_mark) + +{ + ctx->entry = entry; + ctx->max_stack = max_stack; + ctx->nr = entry->nr = 0; + ctx->contexts = 0; + ctx->contexts_maxed = false; + ctx->add_mark = add_mark; +} + +void __get_perf_callchain_kernel(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs) +{ + if (user_mode(regs)) + return; + + if (ctx->add_mark) + perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL); + perf_callchain_kernel(ctx, regs); +} + +void __get_perf_callchain_user(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs) +{ + int start_entry_idx; + + if (!user_mode(regs)) { + if (current->flags & (PF_KTHREAD | PF_USER_WORKER)) + return; + regs = task_pt_regs(current); + } + + if (ctx->add_mark) + perf_callchain_store_context(ctx, PERF_CONTEXT_USER); + + start_entry_idx = entry->nr; + perf_callchain_user(ctx, regs); + fixup_uretprobe_trampoline_entries(entry, start_entry_idx); +} + struct perf_callchain_entry * get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, - u32 max_stack, bool crosstask, bool add_mark) + u32 max_stack, bool crosstask) { - struct perf_callchain_entry *entry; struct perf_callchain_entry_ctx ctx; - int rctx, start_entry_idx; + struct perf_callchain_entry *entry; + int rctx; /* crosstask is not supported for user stacks */ if (crosstask && user && !kernel) return NULL; - entry = get_callchain_entry(&rctx); + entry = get_callchain_entry(&rctx, regs); if (!entry) return NULL; - ctx.entry = entry; - ctx.max_stack = max_stack; - ctx.nr = entry->nr = 0; - ctx.contexts = 0; - ctx.contexts_maxed = false; + __init_perf_callchain_ctx(&ctx, entry, max_stack, true); - if (kernel && !user_mode(regs)) { - if (add_mark) - perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL); - perf_callchain_kernel(&ctx, regs); - } + if (kernel) + __get_perf_callchain_kernel(&ctx, regs); + if (user && !crosstask) + __get_perf_callchain_user(&ctx, regs); - if (user && !crosstask) { - if (!user_mode(regs)) { - if (current->flags & (PF_KTHREAD | PF_USER_WORKER)) - goto exit_put; - regs = task_pt_regs(current); - } - - if (add_mark) - perf_callchain_store_context(&ctx, PERF_CONTEXT_USER); - - start_entry_idx = entry->nr; - perf_callchain_user(&ctx, regs); - fixup_uretprobe_trampoline_entries(entry, start_entry_idx); - } - -exit_put: put_callchain_entry(rctx); return entry; diff --git a/kernel/events/core.c b/kernel/events/core.c index 177e57c1a362..cbe073d761a8 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8218,7 +8218,7 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs) return &__empty_callchain; callchain = get_perf_callchain(regs, kernel, user, - max_stack, crosstask, true); + max_stack, crosstask); return callchain ?: &__empty_callchain; }