From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C6236D7976B for ; Sat, 31 Jan 2026 13:29:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:Cc:To:From: Subject:Message-ID:References:Mime-Version:In-Reply-To:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=uj+W/fw6jviNtcb7rjWbgliWocDtdFOtxpsoa7nbJ6s=; b=VazQmW6QADzDgb2Ko5YQAb+qCF zoum+89MH1AVLkzjHkum+MhD3Nte3wdDBDVREiUYEyRAiCElLkBoJN1e7AmdnfsN9FHENoZDMDzZQ 2TBiNu6GhA+nKVD2qN+HDxwOu72JoPyJiSDM5xidWKKaZpKLJKBsS8+6E/z8vLRSPAxCuTCLwCo3k foej3EyDUyn5vA5BByAFmQQuH2Urr+/l3ve/EptX79y5N8cN0HOxR+qZbbeuj8umOPh9FetBJDmxb 0eM6B40zuv1/EyefFu/r4J0K/WqI6zlDZfXp+J0B+ddU2sAGPJDE/fouMc+HKDN6/iodZtEpuptdh 9b+Z49yw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vmB2g-00000002bvz-0hz9; Sat, 31 Jan 2026 13:29:38 +0000 Received: from mail-wm1-x349.google.com ([2a00:1450:4864:20::349]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vmB2V-00000002bpK-33jm for linux-arm-kernel@lists.infradead.org; Sat, 31 Jan 2026 13:29:28 +0000 Received: by mail-wm1-x349.google.com with SMTP id 5b1f17b1804b1-4806cfffca6so32374425e9.2 for ; Sat, 31 Jan 2026 05:29:26 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1769866165; x=1770470965; darn=lists.infradead.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=uj+W/fw6jviNtcb7rjWbgliWocDtdFOtxpsoa7nbJ6s=; b=mmXKQpXDnMtDC1jSJ1/lU1vZ2uO3WsVh2qkKOyLwZWG2zahZZDMu6AhRb1MrBm13Ao EwFkurS3Zcxbczd3cQnzBoBjmI+Rj3YdC8R4+DlwJH3dqDkkrqTym+Vo2/sos+nGWE1L 01Ju+UtImrfTnwjpLJvr9cx1PnGmrtJr8uJ+ncgzmmTwDjDMuqWMgQppIQBuyoVt1oQ7 YhMy3jiXPHVBAzNetm8EhzC44DyV3HKlf1wYQszo54/eM0zpVhoq1/ToCRTgiHaM9aSP /wD3tYzy1/eY4axWzrX8yu3l5AXxt7jQSjs2tjeqRIko9oPaKi1xu0Wpmtxr+5rySEHf TrhQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769866165; x=1770470965; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=uj+W/fw6jviNtcb7rjWbgliWocDtdFOtxpsoa7nbJ6s=; b=Mi2s5XNjTN9jR4DBpC3HsWVZ0tK7AUTmzVSru9mR3MzMm5BEqzY+mfdKHTgb+WPO9Y 2vHEGpwpf6G9CCebwp3ZnSbYNCMI8X3DF9jOAhH026QzAidoGo1sT/lp/HBjBM6StV9D U/qqJzoqFziCIcYJOchbT24knA/7BMn+d8ZmSjW8bUBSDMACwaldV7YXsfoQxmFrhjwj H97D5SDJ2Q6wVY2MyNOje9cJlmXrC8NcY66f6vf5//WbCrGyHgxQyXXdRYmGceCl/b8/ Gml253iyzumbP3rWThJOZRrMrV4ac7r/Eqs84U3olLQCya2YJM6PBFKnllpzqXi9Lc00 oXmQ== X-Forwarded-Encrypted: i=1; AJvYcCUhPjyQ3PtUVjp8lrHDvIgCVM3A4MLlqRNHNRcXjy4J/st+YF7FJeP3RMvfZGoZfT1vltcRmLnYlv80enPUf/z4@lists.infradead.org X-Gm-Message-State: AOJu0Yzc8UiLyIBoJwJO4uHwwkg7au6TBPFWK4MykF01MXI7sxuPWoG7 SjJBbWeUjkCxE1voGle1zg69aL2M03NbwA0ijNymYyBorRsOu+ohtcM1ADhr0PPh8dijQRF78QU IoaVI2CHOWu5bKrE2SMyoZw== X-Received: from wmju1.prod.google.com ([2002:a7b:cb01:0:b0:480:6b8b:a7ab]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:8b42:b0:477:5af7:6fa with SMTP id 5b1f17b1804b1-482db49728bmr62880405e9.32.1769866165397; Sat, 31 Jan 2026 05:29:25 -0800 (PST) Date: Sat, 31 Jan 2026 13:28:22 +0000 In-Reply-To: <20260131132848.254084-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20260131132848.254084-1-vdonnefort@google.com> X-Mailer: git-send-email 2.53.0.rc1.225.gd81095ad13-goog Message-ID: <20260131132848.254084-5-vdonnefort@google.com> Subject: [PATCH v11 04/30] ring-buffer: Add non-consuming read for ring-buffer remotes From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, jstultz@google.com, qperret@google.com, will@kernel.org, aneesh.kumar@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260131_052927_789165_1D632B0A X-CRM114-Status: GOOD ( 13.64 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hopefully, the remote will only swap pages on the kernel instruction (via the swap_reader_page() callback). This means we know at what point the ring-buffer geometry has changed. It is therefore possible to rearrange the kernel view of that ring-buffer to allow non-consuming read. Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 00754339733d..2d08dd326309 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5365,10 +5365,51 @@ static bool rb_read_remote_meta_page(struct ring_buffer_per_cpu *cpu_buffer) return rb_num_of_entries(cpu_buffer); } +static void rb_update_remote_head(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct buffer_page *next, *orig; + int retry = 3; + + orig = next = cpu_buffer->head_page; + rb_inc_page(&next); + + /* Run after the writer */ + while (cpu_buffer->head_page->page->time_stamp > next->page->time_stamp) { + rb_inc_page(&next); + + rb_list_head_clear(cpu_buffer->head_page->list.prev); + rb_inc_page(&cpu_buffer->head_page); + rb_set_list_to_head(cpu_buffer->head_page->list.prev); + + if (cpu_buffer->head_page == orig) { + if (WARN_ON_ONCE(!(--retry))) + return; + } + } + + orig = cpu_buffer->commit_page = cpu_buffer->head_page; + retry = 3; + + while (cpu_buffer->commit_page->page->time_stamp < next->page->time_stamp) { + rb_inc_page(&next); + rb_inc_page(&cpu_buffer->commit_page); + + if (cpu_buffer->commit_page == orig) { + if (WARN_ON_ONCE(!(--retry))) + return; + } + } +} + static void rb_iter_reset(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; + if (cpu_buffer->remote) { + rb_read_remote_meta_page(cpu_buffer); + rb_update_remote_head(cpu_buffer); + } + /* Iterator usage is expected to have record disabled */ iter->head_page = cpu_buffer->reader_page; iter->head = cpu_buffer->reader_page->read; @@ -5521,7 +5562,7 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter, static struct buffer_page * __rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer) { - struct buffer_page *new_reader, *prev_reader; + struct buffer_page *new_reader, *prev_reader, *prev_head, *new_head, *last; if (!rb_read_remote_meta_page(cpu_buffer)) return NULL; @@ -5545,10 +5586,32 @@ __rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer) WARN_ON_ONCE(prev_reader == new_reader); - cpu_buffer->reader_page->page = new_reader->page; - cpu_buffer->reader_page->id = new_reader->id; - cpu_buffer->reader_page->read = 0; - cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp; + prev_head = new_reader; /* New reader was also the previous head */ + new_head = prev_head; + rb_inc_page(&new_head); + last = prev_head; + rb_dec_page(&last); + + /* Clear the old HEAD flag */ + rb_list_head_clear(cpu_buffer->head_page->list.prev); + + prev_reader->list.next = prev_head->list.next; + prev_reader->list.prev = prev_head->list.prev; + + /* Swap prev_reader with new_reader */ + last->list.next = &prev_reader->list; + new_head->list.prev = &prev_reader->list; + + new_reader->list.prev = &new_reader->list; + new_reader->list.next = &new_head->list; + + /* Reactivate the HEAD flag */ + rb_set_list_to_head(&last->list); + + cpu_buffer->head_page = new_head; + cpu_buffer->reader_page = new_reader; + cpu_buffer->pages = &new_head->list; + cpu_buffer->read_stamp = new_reader->page->time_stamp; cpu_buffer->lost_events = cpu_buffer->meta_page->reader.lost_events; return rb_page_size(cpu_buffer->reader_page) ? cpu_buffer->reader_page : NULL; @@ -6132,7 +6195,7 @@ ring_buffer_read_start(struct trace_buffer *buffer, int cpu, gfp_t flags) struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_iter *iter; - if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->remote) + if (!cpumask_test_cpu(cpu, buffer->cpumask)) return NULL; iter = kzalloc(sizeof(*iter), flags); -- 2.53.0.rc1.225.gd81095ad13-goog