From: Valentin Schneider <vschneid@redhat.com>
To: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-snps-arc@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org,
linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
loongarch@lists.linux.dev, linux-mips@vger.kernel.org,
openrisc@lists.librecores.org, linux-parisc@vger.kernel.org,
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linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
x86@kernel.org
Cc: Juri Lelli <juri.lelli@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Marc Zyngier <maz@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Marcelo Tosatti <mtosatti@redhat.com>,
Russell King <linux@armlinux.org.uk>,
Steven Rostedt <rostedt@goodmis.org>,
"David S. Miller" <davem@davemloft.net>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Nicholas Piggin <npiggin@gmail.com>,
"H. Peter Anvin" <hpa@zytor.com>, Guo Ren <guoren@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>
Subject: [RFC PATCH 0/5] Generic IPI sending tracepoint
Date: Fri, 7 Oct 2022 16:41:40 +0100 [thread overview]
Message-ID: <20221007154145.1877054-1-vschneid@redhat.com> (raw)
Background
==========
Detecting IPI *reception* is relatively easy, e.g. using
trace_irq_handler_{entry,exit} or even just function-trace
flush_smp_call_function_queue() for SMP calls.
Figuring out their *origin*, is trickier as there is no generic tracepoint tied
to e.g. smp_call_function():
o AFAIA x86 has no tracepoint tied to sending IPIs, only receiving them
(cf. trace_call_function{_single}_entry()).
o arm/arm64 do have trace_ipi_raise(), which gives us the target cpus but also a
mostly useless string (smp_calls will all be "Function call interrupts").
o Other architectures don't seem to have any IPI-sending related tracepoint.
I believe one reason those tracepoints used by arm/arm64 ended up as they were
is because these archs used to handle IPIs differently from regular interrupts
(the IRQ driver would directly invoke an IPI-handling routine), which meant they
never showed up in trace_irq_handler_{entry, exit}. The trace_ipi_{entry,exit}
tracepoints gave a way to trace IPI reception but those have become redundant as
of:
56afcd3dbd19 ("ARM: Allow IPIs to be handled as normal interrupts")
d3afc7f12987 ("arm64: Allow IPIs to be handled as normal interrupts")
which gave IPIs a "proper" handler function used through
generic_handle_domain_irq(), which makes them show up via
trace_irq_handler_{entry, exit}.
Changing stuff up
=================
Per the above, it would make sense to reshuffle trace_ipi_raise() and move it
into generic code. This also came up during Daniel's talk on Osnoise at the CPU
isolation MC of LPC 2022 [1].
Now, to be useful, such a tracepoint needs to export:
o targeted CPU(s)
o calling context
The only way to get the calling context with trace_ipi_raise() is to trigger a
stack dump, e.g. $(trace-cmd -e ipi* -T echo 42).
As for the targeted CPUs, the existing tracepoint does export them, albeit in
cpumask form, which is quite inconvenient from a tooling perspective. For
instance, as far as I'm aware, it's not possible to do event filtering on a
cpumask via trace-cmd.
Because of the above points, this is introducing a new tracepoint.
Patches
=======
This results in having trace events for:
o smp_call_function*()
o smp_send_reschedule()
o irq_work_queue*()
This is incomplete, just looking at arm64 there's more IPI types that aren't covered:
IPI_CPU_STOP,
IPI_CPU_CRASH_STOP,
IPI_TIMER,
IPI_WAKEUP,
... But it feels like a good starting point.
Another thing worth mentioning is that depending on the callsite, the _RET_IP_
fed to the tracepoint is not always useful - generic_exec_single() doesn't tell
you much about the actual callback being sent via IPI, so there might be value
in exploding the single tracepoint into at least one variant for smp_calls.
Links
=====
[1]: https://youtu.be/5gT57y4OzBM?t=14234
Valentin Schneider (5):
trace: Add trace_ipi_send_{cpu, cpumask}
sched, smp: Trace send_call_function_single_ipi()
smp: Add a multi-CPU variant to send_call_function_single_ipi()
irq_work: Trace calls to arch_irq_work_raise()
treewide: Rename and trace arch-definitions of smp_send_reschedule()
arch/alpha/kernel/smp.c | 2 +-
arch/arc/kernel/smp.c | 2 +-
arch/arm/kernel/smp.c | 5 +----
arch/arm64/kernel/smp.c | 3 +--
arch/csky/kernel/smp.c | 2 +-
arch/hexagon/kernel/smp.c | 2 +-
arch/ia64/kernel/smp.c | 4 ++--
arch/loongarch/include/asm/smp.h | 2 +-
arch/mips/include/asm/smp.h | 2 +-
arch/openrisc/kernel/smp.c | 2 +-
arch/parisc/kernel/smp.c | 4 ++--
arch/powerpc/kernel/smp.c | 4 ++--
arch/riscv/kernel/smp.c | 4 ++--
arch/s390/kernel/smp.c | 2 +-
arch/sh/kernel/smp.c | 2 +-
arch/sparc/kernel/smp_32.c | 2 +-
arch/sparc/kernel/smp_64.c | 2 +-
arch/x86/include/asm/smp.h | 2 +-
arch/xtensa/kernel/smp.c | 2 +-
include/linux/smp.h | 1 +
include/trace/events/ipi.h | 27 +++++++++++++++++++++++++++
kernel/irq_work.c | 12 +++++++++++-
kernel/sched/core.c | 7 +++++--
kernel/smp.c | 18 +++++++++++++++++-
24 files changed, 84 insertions(+), 31 deletions(-)
--
2.31.1
next reply other threads:[~2022-10-08 1:30 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-07 15:41 Valentin Schneider [this message]
2022-10-07 15:45 ` [RFC PATCH 1/5] trace: Add trace_ipi_send_{cpu, cpumask} Valentin Schneider
2022-10-07 15:45 ` [RFC PATCH 2/5] sched, smp: Trace send_call_function_single_ipi() Valentin Schneider
2022-10-07 15:45 ` [RFC PATCH 3/5] smp: Add a multi-CPU variant to send_call_function_single_ipi() Valentin Schneider
2022-10-07 15:45 ` [RFC PATCH 4/5] irq_work: Trace calls to arch_irq_work_raise() Valentin Schneider
2022-10-08 19:34 ` Steven Rostedt
2022-10-11 15:02 ` Valentin Schneider
2022-10-07 15:45 ` [RFC PATCH 5/5] treewide: Rename and trace arch-definitions of smp_send_reschedule() Valentin Schneider
2022-10-08 0:23 ` Guo Ren
2022-10-07 20:01 ` [RFC PATCH 0/5] Generic IPI sending tracepoint Marcelo Tosatti
2022-10-08 19:40 ` Steven Rostedt
2022-10-11 16:17 ` Valentin Schneider
2022-10-11 16:22 ` Daniel Bristot de Oliveira
2022-10-11 16:40 ` Valentin Schneider
2022-10-11 20:41 ` Steven Rostedt
2022-10-11 20:34 ` Steven Rostedt
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