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authorLinus Torvalds2024-01-18 14:35:29 -0800
committerLinus Torvalds2024-01-18 14:35:29 -0800
commita2ded784cd7fd83e567829637068cd86aeffbeaf (patch)
tree9924ca8854858fc5558e59b136d1f32695bc8cc4 /Documentation
parent5b890ad456b16a5b45e7f86d9708d7248e73d0f8 (diff)
parent25742aeb135c4a44e92fb347e037adaa145b9484 (diff)
Merge tag 'trace-v6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing updates from Steven Rostedt: - Allow kernel trace instance creation to specify what events are created Inside the kernel, a subsystem may create a tracing instance that it can use to send events to user space. This sub-system may not care about the thousands of events that exist in eventfs. Allow the sub-system to specify what sub-systems of events it cares about, and only those events are exposed to this instance. - Allow the ring buffer to be broken up into bigger sub-buffers than just the architecture page size. A new tracefs file called "buffer_subbuf_size_kb" is created. The user can now specify a minimum size the sub-buffer may be in kilobytes. Note, that the implementation currently make the sub-buffer size a power of 2 pages (1, 2, 4, 8, 16, ...) but the user only writes in kilobyte size, and the sub-buffer will be updated to the next size that it will can accommodate it. If the user writes in 10, it will change the size to be 4 pages on x86 (16K), as that is the next available size that can hold 10K pages. - Update the debug output when a corrupt time is detected in the ring buffer. If the ring buffer detects inconsistent timestamps, there's a debug config options that will dump the contents of the meta data of the sub-buffer that is used for debugging. Add some more information to this dump that helps with debugging. - Add more timestamp debugging checks (only triggers when the config is enabled) - Increase the trace_seq iterator to 2 page sizes. - Allow strings written into tracefs_marker to be larger. Up to just under 2 page sizes (based on what trace_seq can hold). - Increase the trace_maker_raw write to be as big as a sub-buffer can hold. - Remove 32 bit time stamp logic, now that the rb_time_cmpxchg() has been removed. - More selftests were added. - Some code clean ups as well. * tag 'trace-v6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (29 commits) ring-buffer: Remove stale comment from ring_buffer_size() tracing histograms: Simplify parse_actions() function tracing/selftests: Remove exec permissions from trace_marker.tc test ring-buffer: Use subbuf_order for buffer page masking tracing: Update subbuffer with kilobytes not page order ringbuffer/selftest: Add basic selftest to test changing subbuf order ring-buffer: Add documentation on the buffer_subbuf_order file ring-buffer: Just update the subbuffers when changing their allocation order ring-buffer: Keep the same size when updating the order tracing: Stop the tracing while changing the ring buffer subbuf size tracing: Update snapshot order along with main buffer order ring-buffer: Make sure the spare sub buffer used for reads has same size ring-buffer: Do no swap cpu buffers if order is different ring-buffer: Clear pages on error in ring_buffer_subbuf_order_set() failure ring-buffer: Read and write to ring buffers with custom sub buffer size ring-buffer: Set new size of the ring buffer sub page ring-buffer: Add interface for configuring trace sub buffer size ring-buffer: Page size per ring buffer ring-buffer: Have ring_buffer_print_page_header() be able to access ring_buffer_iter ring-buffer: Check if absolute timestamp goes backwards ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/trace/ftrace.rst21
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 16122a8895ba..7e7b8ec17934 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -218,6 +218,27 @@ of ftrace. Here is a list of some of the key files:
This displays the total combined size of all the trace buffers.
+ buffer_subbuf_size_kb:
+
+ This sets or displays the sub buffer size. The ring buffer is broken up
+ into several same size "sub buffers". An event can not be bigger than
+ the size of the sub buffer. Normally, the sub buffer is the size of the
+ architecture's page (4K on x86). The sub buffer also contains meta data
+ at the start which also limits the size of an event. That means when
+ the sub buffer is a page size, no event can be larger than the page
+ size minus the sub buffer meta data.
+
+ Note, the buffer_subbuf_size_kb is a way for the user to specify the
+ minimum size of the subbuffer. The kernel may make it bigger due to the
+ implementation details, or simply fail the operation if the kernel can
+ not handle the request.
+
+ Changing the sub buffer size allows for events to be larger than the
+ page size.
+
+ Note: When changing the sub-buffer size, tracing is stopped and any
+ data in the ring buffer and the snapshot buffer will be discarded.
+
free_buffer:
If a process is performing tracing, and the ring buffer should be