Steven Rostedt
ac7ab38c27
[ Upstream commit7ab0fc61ce] The histogram trigger has three somewhat large arrays on the kernel stack: unsigned long entries[HIST_STACKTRACE_DEPTH]; u64 var_ref_vals[TRACING_MAP_VARS_MAX]; char compound_key[HIST_KEY_SIZE_MAX]; Checking the function event_hist_trigger() stack frame size, it currently uses 816 bytes for its stack frame due to these variables! Instead, allocate a per CPU structure that holds these arrays for each context level (normal, softirq, irq and NMI). That is, each CPU will have 4 of these structures. This will be allocated when the first histogram trigger is enabled and freed when the last is disabled. When the histogram callback triggers, it will request this structure. The request will disable preemption, get the per CPU structure at the index of the per CPU variable, and increment that variable. The callback will use the arrays in this structure to perform its work and then release the structure. That in turn will simply decrement the per CPU index and enable preemption. Moving the variables from the kernel stack to the per CPU structure brings the stack frame of event_hist_trigger() down to just 112 bytes. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Tom Zanussi <zanussi@kernel.org> Link: https://lore.kernel.org/20250407123851.74ea8d58@gandalf.local.home Fixes:067fe038e7("tracing: Add variable reference handling to hist triggers") Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.