| Message ID | 20240105094729.2363579-1-vdonnefort@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Introducing trace buffer mapping by user-space | expand |
Hi Vincent, On Fri, 5 Jan 2024 09:47:27 +0000 Vincent Donnefort <vdonnefort@google.com> wrote: > The tracing ring-buffers can be stored on disk or sent to network > without any copy via splice. However the later doesn't allow real time > processing of the traces. A solution is to give userspace direct access > to the ring-buffer pages via a mapping. An application can now become a > consumer of the ring-buffer, in a similar fashion to what trace_pipe > offers. I think this is very nice feature. But this series seems just a feature, no document and no example code. Can you add 2 patches to add those? I know libtracefs already provide a support code, but I think it is better to have a test code under tools/testing/selftests/ring_buffer. I also wonder what happen if other operation (e.g. taking snapshot) happens while mmaping the ring buffer. Thank you, > > Support for this new feature in libtracefs can be found here: > > https://lore.kernel.org/all/20231228201100.78aae259@rorschach.local.home > > Vincent > > v9 -> v10: > * Refactor rb_update_meta_page() > * In-loop declaration for foreach_subbuf_page() > * Check for cpu_buffer->mapped overflow > > v8 -> v9: > * Fix the unlock path in ring_buffer_map() > * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer > * Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a) > > v7 -> v8: > * Drop the subbufs renaming into bpages > * Use subbuf as a name when relevant > > v6 -> v7: > * Rebase onto lore.kernel.org/lkml/20231215175502.106587604@goodmis.org/ > * Support for subbufs > * Rename subbufs into bpages > > v5 -> v6: > * Rebase on next-20230802. > * (unsigned long) -> (void *) cast for virt_to_page(). > * Add a wait for the GET_READER_PAGE ioctl. > * Move writer fields update (overrun/pages_lost/entries/pages_touched) > in the irq_work. > * Rearrange id in struct buffer_page. > * Rearrange the meta-page. > * ring_buffer_meta_page -> trace_buffer_meta_page. > * Add meta_struct_len into the meta-page. > > v4 -> v5: > * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3) > > v3 -> v4: > * Add to the meta-page: > - pages_lost / pages_read (allow to compute how full is the > ring-buffer) > - read (allow to compute how many entries can be read) > - A reader_page struct. > * Rename ring_buffer_meta_header -> ring_buffer_meta > * Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page > * Properly consume events on ring_buffer_map_get_reader_page() with > rb_advance_reader(). > > v2 -> v3: > * Remove data page list (for non-consuming read) > ** Implies removing order > 0 meta-page > * Add a new meta page field ->read > * Rename ring_buffer_meta_page_header into ring_buffer_meta_header > > v1 -> v2: > * Hide data_pages from the userspace struct > * Fix META_PAGE_MAX_PAGES > * Support for order > 0 meta-page > * Add missing page->mapping. > > --- > > Vincent Donnefort (2): > ring-buffer: Introducing ring-buffer mapping functions > tracing: Allow user-space mapping of the ring-buffer > > include/linux/ring_buffer.h | 7 + > include/uapi/linux/trace_mmap.h | 31 +++ > kernel/trace/ring_buffer.c | 384 +++++++++++++++++++++++++++++++- > kernel/trace/trace.c | 79 ++++++- > 4 files changed, 497 insertions(+), 4 deletions(-) > create mode 100644 include/uapi/linux/trace_mmap.h > > > base-commit: 3cb3091138ca0921c4569bcf7ffa062519639b6a > -- > 2.43.0.472.g3155946c3a-goog > >
Hi Masami, thanks for looking at this. On Tue, 9 Jan 2024 22:04:45 +0900 Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > The tracing ring-buffers can be stored on disk or sent to network > > without any copy via splice. However the later doesn't allow real time > > processing of the traces. A solution is to give userspace direct access > > to the ring-buffer pages via a mapping. An application can now become a > > consumer of the ring-buffer, in a similar fashion to what trace_pipe > > offers. > > I think this is very nice feature. But this series seems just a feature, > no document and no example code. Can you add 2 patches to add those? > I know libtracefs already provide a support code, but I think it is > better to have a test code under tools/testing/selftests/ring_buffer. Yeah, we should have sample code and a test. > > I also wonder what happen if other operation (e.g. taking snapshot) happens > while mmaping the ring buffer. Hmm, good point. We should disable snapshots when mapped, and also prevent mapping with latency tracer if we are not already doing that. -- Steve
On Tue, Jan 09, 2024 at 08:20:57AM -0500, Steven Rostedt wrote: > > Hi Masami, thanks for looking at this. > > On Tue, 9 Jan 2024 22:04:45 +0900 > Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > > > The tracing ring-buffers can be stored on disk or sent to network > > > without any copy via splice. However the later doesn't allow real time > > > processing of the traces. A solution is to give userspace direct access > > > to the ring-buffer pages via a mapping. An application can now become a > > > consumer of the ring-buffer, in a similar fashion to what trace_pipe > > > offers. > > > > I think this is very nice feature. But this series seems just a feature, > > no document and no example code. Can you add 2 patches to add those? > > I know libtracefs already provide a support code, but I think it is > > better to have a test code under tools/testing/selftests/ring_buffer. > > Yeah, we should have sample code and a test. Ack. I will recycle what I had in the cover letter in a ring_buffer selftest. > > > > > I also wonder what happen if other operation (e.g. taking snapshot) happens > > while mmaping the ring buffer. > > Hmm, good point. We should disable snapshots when mapped, and also prevent > mapping with latency tracer if we are not already doing that. ring_buffer_swap_cpu() is already disabled when mapped as well as resize_disabled set. Is something else necessary? > > -- Steve
The tracing ring-buffers can be stored on disk or sent to network without any copy via splice. However the later doesn't allow real time processing of the traces. A solution is to give userspace direct access to the ring-buffer pages via a mapping. An application can now become a consumer of the ring-buffer, in a similar fashion to what trace_pipe offers. Support for this new feature in libtracefs can be found here: https://lore.kernel.org/all/20231228201100.78aae259@rorschach.local.home Vincent v9 -> v10: * Refactor rb_update_meta_page() * In-loop declaration for foreach_subbuf_page() * Check for cpu_buffer->mapped overflow v8 -> v9: * Fix the unlock path in ring_buffer_map() * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer * Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a) v7 -> v8: * Drop the subbufs renaming into bpages * Use subbuf as a name when relevant v6 -> v7: * Rebase onto lore.kernel.org/lkml/20231215175502.106587604@goodmis.org/ * Support for subbufs * Rename subbufs into bpages v5 -> v6: * Rebase on next-20230802. * (unsigned long) -> (void *) cast for virt_to_page(). * Add a wait for the GET_READER_PAGE ioctl. * Move writer fields update (overrun/pages_lost/entries/pages_touched) in the irq_work. * Rearrange id in struct buffer_page. * Rearrange the meta-page. * ring_buffer_meta_page -> trace_buffer_meta_page. * Add meta_struct_len into the meta-page. v4 -> v5: * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3) v3 -> v4: * Add to the meta-page: - pages_lost / pages_read (allow to compute how full is the ring-buffer) - read (allow to compute how many entries can be read) - A reader_page struct. * Rename ring_buffer_meta_header -> ring_buffer_meta * Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page * Properly consume events on ring_buffer_map_get_reader_page() with rb_advance_reader(). v2 -> v3: * Remove data page list (for non-consuming read) ** Implies removing order > 0 meta-page * Add a new meta page field ->read * Rename ring_buffer_meta_page_header into ring_buffer_meta_header v1 -> v2: * Hide data_pages from the userspace struct * Fix META_PAGE_MAX_PAGES * Support for order > 0 meta-page * Add missing page->mapping. --- Vincent Donnefort (2): ring-buffer: Introducing ring-buffer mapping functions tracing: Allow user-space mapping of the ring-buffer include/linux/ring_buffer.h | 7 + include/uapi/linux/trace_mmap.h | 31 +++ kernel/trace/ring_buffer.c | 384 +++++++++++++++++++++++++++++++- kernel/trace/trace.c | 79 ++++++- 4 files changed, 497 insertions(+), 4 deletions(-) create mode 100644 include/uapi/linux/trace_mmap.h base-commit: 3cb3091138ca0921c4569bcf7ffa062519639b6a