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[35.195.29.211]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e752238832sm6017788f8f.31.2025.09.10.02.47.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Sep 2025 02:47:57 -0700 (PDT) Date: Wed, 10 Sep 2025 10:47:54 +0100 From: Vincent Donnefort To: Steven Rostedt Cc: 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, 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 Subject: Re: [PATCH v6 10/24] tracing: Introduce simple_ring_buffer Message-ID: References: <20250821081412.1008261-1-vdonnefort@google.com> <20250821081412.1008261-11-vdonnefort@google.com> <20250909182644.092b3e85@gandalf.local.home> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250909182644.092b3e85@gandalf.local.home> [...] > > +static struct ring_buffer_event * > > +simple_rb_reserve_next(struct simple_rb_per_cpu *cpu_buffer, unsigned long length, u64 timestamp) > > +{ > > + unsigned long ts_ext_size = 0, event_size = rb_event_size(length); > > + struct simple_buffer_page *tail = cpu_buffer->tail_page; > > + struct ring_buffer_event *event; > > + u32 write, prev_write; > > + u64 time_delta; > > + > > + time_delta = timestamp - cpu_buffer->write_stamp; > > The remote buffers never get preempted do they? > > That is, it doesn't need to handle different contexts like the normal > kernel does? (normal, softirq, irq, NMI, etc). No, luckily, we don't need to support any of that. > > -- Steve > > > + > > + if (test_time_stamp(time_delta)) > > + ts_ext_size = 8; > > + > > + prev_write = tail->write; > > + write = prev_write + event_size + ts_ext_size; > > + > > + if (unlikely(write > (PAGE_SIZE - BUF_PAGE_HDR_SIZE))) > > + tail = simple_rb_move_tail(cpu_buffer); > > + > > + if (!tail->entries) { > > + tail->page->time_stamp = timestamp; > > + time_delta = 0; > > + ts_ext_size = 0; > > + write = event_size; > > + prev_write = 0; > > + } > > + > > + tail->write = write; > > + tail->entries++; > > + > > + cpu_buffer->write_stamp = timestamp; > > + > > + event = (struct ring_buffer_event *)(tail->page->data + prev_write); > > + if (ts_ext_size) { > > + event = rb_event_add_ts_extend(event, time_delta); > > + time_delta = 0; > > + } > > + > > + event->type_len = 0; > > + event->time_delta = time_delta; > > + event->array[0] = event_size - RB_EVNT_HDR_SIZE; > > + > > + return event; > > +} > > +