Re: [PATCH v3 0/3] tracing: Read user data from futex system call trace event

[Steven Rostedt]

Peter,

Any thoughts on this version?

-- Steve


On Tue, 31 Mar 2026 14:13:49 -0400
Steven Rostedt <rostedt@xxxxxxxxxx> wrote:

> We are looking at the performance of futexes and require a bit more
> information when tracing them.
> 
> The two patches here extend the system call reading of user space to
> create specific handling of the futex system call. It now reads the
> user space relevant data (the addr, utime and addr2), as well as
> parses the flags. This adds a little smarts to the trace event as
> it only shows the parameters that are relevant, as well as parses
> utime as either a timespec or as val2 depending on the futex_op.
> 
> Here's an example of the new output:
> 
>  sys_futex(uaddr: 0x56196292e830 (0), FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
>  sys_futex(uaddr: 0x56196292e834 (0x4a7) tid: 1191, FUTEX_UNLOCK_PI|FUTEX_PRIVATE_FLAG)
>  sys_futex(uaddr: 0x56196292e834 (0) tid: 0, FUTEX_LOCK_PI|FUTEX_PRIVATE_FLAG)
>  sys_futex(uaddr: 0x56196292e830 (0), FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
>  sys_futex(uaddr: 0x56196292e838 (0), FUTEX_WAIT_REQUEUE_PI|FUTEX_PRIVATE_FLAG, timespec: 0x7ffc1b91a9f0 (163.048528790), uaddr2: 0x56196292e834 (4aa), val3: 0)
>  sys_futex(uaddr: 0x56196292e834 (0x4aa) tid: 1194, FUTEX_LOCK_PI|FUTEX_PRIVATE_FLAG)
>  sys_futex(uaddr: 0x56196292e838 (0), FUTEX_WAIT_REQUEUE_PI|FUTEX_PRIVATE_FLAG, timespec: 0x7ffc1b91a9f0 (163.048528790), uaddr2: 0x56196292e834 (800004aa), val3: 0)
>  sys_futex(uaddr: 0x7f7ed6b29990 (0x4ab), FUTEX_WAIT_BITSET|FUTEX_CLOCK_REALTIME)
>  sys_futex(uaddr: 0x56196292e834 (0x800004aa) tid: 1194 (WAITERS), FUTEX_LOCK_PI|FUTEX_PRIVATE_FLAG)
>  sys_futex(uaddr: 0x56196292e838 (0), FUTEX_WAIT_REQUEUE_PI|FUTEX_PRIVATE_FLAG, timespec: 0x7ffc1b91a9f0 (163.048528790), uaddr2: 0x56196292e834 (800004aa), val3: 0)
>  sys_futex(uaddr: 0x56196292e834 (0x800004aa) tid: 1194 (WAITERS), FUTEX_LOCK_PI|FUTEX_PRIVATE_FLAG)
> 
> Changes since v2: https://lore.kernel.org/all/20260310200954.285663884@xxxxxxxxxx/
> 
> - Removed unused "buf" variable (kernel test robot)
> 
> - Iterate __futex_cmds[] make the print statement.
>   Note this required exposing __futex_cmds[] to trace_syscall.c
>   (Masami Hiramatsu)
> 
> - Added back val statement (with the move to futex/syscall.c the
>   third parameter was dropped).
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
> futex/core
> 
> Head SHA1: 79b0609ad15b24d0bbfb1790e17902a6c210ae69
> 
> 
> Steven Rostedt (3):
>       tracing: Have futex syscall trace event show specific user data
>       tracing: Update futex syscall trace event to show more commands
>       tracing: Show TID and flags for PI futex system call trace event
> 
> ----
>  include/linux/futex.h         |  39 ++++++-
>  kernel/futex/syscalls.c       | 137 +++++++++++++++++++++---
>  kernel/trace/trace_syscalls.c | 237 +++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 396 insertions(+), 17 deletions(-)