Peter, can you take a look at these patches please. I believe you're the
only one that really maintains this code today.
-- Steve
On Mon, 08 Sep 2025 13:14:12 -0400
Steven Rostedt <rostedt@kernel.org> wrote:
> [
> This is simply a resend of version 15 of this patch series
> but with only the kernel changes. I'm separating out the user space
> changes to their own series.
> The original v15 is here:
> https://lore.kernel.org/linux-trace-kernel/20250825180638.877627656@kernel.org/
> ]
>
> This patch set is based off of perf/core of the tip tree:
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
>
> To run this series, you can checkout this repo that has this series as well as the above:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git unwind/perf-test
>
> This series implements the perf interface to use deferred user space stack
> tracing.
>
> Patch 1 adds a new API interface to the user unwinder logic to allow perf to
> get the current context cookie for it's task event tracing. Perf's task event
> tracing maps a single task per perf event buffer and it follows the task
> around, so it only needs to implement its own task_work to do the deferred
> stack trace. Because it can still suffer not knowing which user stack trace
> belongs to which kernel stack due to dropped events, having the cookie to
> create a unique identifier for each user space stack trace to know which
> kernel stack to append it to is useful.
>
> Patch 2 adds the per task deferred stack traces to perf. It adds a new event
> type called PERF_RECORD_CALLCHAIN_DEFERRED that is recorded when a task is
> about to go back to user space and happens in a location that pages may be
> faulted in. It also adds a new callchain context called PERF_CONTEXT_USER_DEFERRED
> that is used as a place holder in a kernel callchain to append the deferred
> user space stack trace to.
>
> Patch 3 adds the user stack trace context cookie in the kernel callchain right
> after the PERF_CONTEXT_USER_DEFERRED context so that the user space side can
> map the request to the deferred user space stack trace.
>
> Patch 4 adds support for the per CPU perf events that will allow the kernel to
> associate each of the per CPU perf event buffers to a single application. This
> is needed so that when a request for a deferred stack trace happens on a task
> that then migrates to another CPU, it will know which CPU buffer to use to
> record the stack trace on. It is possible to have more than one perf user tool
> running and a request made by one perf tool should have the deferred trace go
> to the same perf tool's perf CPU event buffer. A global list of all the
> descriptors representing each perf tool that is using deferred stack tracing
> is created to manage this.
>
>
> Josh Poimboeuf (1):
> perf: Support deferred user callchains
>
> Steven Rostedt (3):
> unwind deferred: Add unwind_user_get_cookie() API
> perf: Have the deferred request record the user context cookie
> perf: Support deferred user callchains for per CPU events
>
> ----
> include/linux/perf_event.h | 11 +-
> include/linux/unwind_deferred.h | 5 +
> include/uapi/linux/perf_event.h | 25 +-
> kernel/bpf/stackmap.c | 4 +-
> kernel/events/callchain.c | 14 +-
> kernel/events/core.c | 421 +++++++++++++++++++++++++++++++++-
> kernel/unwind/deferred.c | 21 ++
> tools/include/uapi/linux/perf_event.h | 25 +-
> 8 files changed, 518 insertions(+), 8 deletions(-)