diff options
| author | Beau Belgrave <beaub@linux.microsoft.com> | 2023-03-28 16:52:10 -0700 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-03-29 06:52:08 -0400 |
| commit | 7235759084a4f8524a46bd2638885ff3b34ce279 (patch) | |
| tree | 047b165381549bdefe985e8cacede251f42dfce4 /kernel/trace/Kconfig | |
| parent | fd593511cdfc0b0e38af2eb21c99f5154a1d7acf (diff) | |
tracing/user_events: Use remote writes for event enablement
As part of the discussions for user_events aligned with user space
tracers, it was determined that user programs should register a aligned
value to set or clear a bit when an event becomes enabled. Currently a
shared page is being used that requires mmap(). Remove the shared page
implementation and move to a user registered address implementation.
In this new model during the event registration from user programs 3 new
values are specified. The first is the address to update when the event
is either enabled or disabled. The second is the bit to set/clear to
reflect the event being enabled. The third is the size of the value at
the specified address.
This allows for a local 32/64-bit value in user programs to support
both kernel and user tracers. As an example, setting bit 31 for kernel
tracers when the event becomes enabled allows for user tracers to use
the other bits for ref counts or other flags. The kernel side updates
the bit atomically, user programs need to also update these values
atomically.
User provided addresses must be aligned on a natural boundary, this
allows for single page checking and prevents odd behaviors such as a
enable value straddling 2 pages instead of a single page. Currently
page faults are only logged, future patches will handle these.
Link: https://lkml.kernel.org/r/20230328235219.203-4-beaub@linux.microsoft.com
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/Kconfig')
| -rw-r--r-- | kernel/trace/Kconfig | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 5b1e7fa41ca8..c7020e071bf9 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -798,9 +798,10 @@ config USER_EVENTS can be used like an existing kernel trace event. User trace events are generated by writing to a tracefs file. User processes can determine if their tracing events should be - generated by memory mapping a tracefs file and checking for - an associated byte being non-zero. + generated by registering a value and bit with the kernel + that reflects when it is enabled or not. + See Documentation/trace/user_events.rst. If in doubt, say N. config HIST_TRIGGERS |