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When the system has many cores and task switching is frequent, setting set_ftrace_pid can cause frequent pid_list->lock contention and high system sys usage. For example, in a 288-core VM environment, we observed 267 CPUs experiencing contention on pid_list->lock, with stack traces showing: #4 [ffffa6226fb4bc70] native_queued_spin_lock_slowpath at ffffffff99cd4b7e #5 [ffffa6226fb4bc90] _raw_spin_lock_irqsave at ffffffff99cd3e36 #6 [ffffa6226fb4bca0] trace_pid_list_is_set at ffffffff99267554 #7 [ffffa6226fb4bcc0] trace_ignore_this_task at ffffffff9925c288 #8 [ffffa6226fb4bcd8] ftrace_filter_pid_sched_switch_probe at ffffffff99246efe #9 [ffffa6226fb4bcf0] __schedule at ffffffff99ccd161 Replaces the existing spinlock with a seqlock to allow concurrent readers, while maintaining write exclusivity. Link: https://patch.msgid.link/20251113000252.1058144-1-leonylgao@gmail.com Reviewed-by: Huang Cun <cunhuang@tencent.com> Signed-off-by: Yongliang Gao <leonylgao@tencent.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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 reStructuredText 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.