Re: [PATCH v2 1/3] tracing: Replace TRACE_FLAG_IRQS_NOSUPPORT with its config option.

From: Steven Rostedt
Date: Tue Oct 22 2024 - 03:15:11 EST


On Mon, 21 Oct 2024 17:08:40 +0200
Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:

> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> The TRACE_FLAG_IRQS_NOSUPPORT flag is used by tracing_gen_ctx.*() to
> signal that CONFIG_TRACE_IRQFLAGS_SUPPORT is not enabled and tracing IRQ
> flags is not supported.
>
> This could be replaced by using the 0 as flags and then deducting that
> there is no IRQFLAGS_SUPPORT based on the config option. The downside is
> that without CONFIG_TRACE_IRQFLAGS_SUPPORT we can not distinguish
> between no-IRQ passed flags and callers which passed 0. On the upside we
> have room for one additional flags which could be used for LAZY_PREEMPTION.
>
> Remove TRACE_FLAG_IRQS_NOSUPPORT and set it flags are 0 and
> CONFIG_TRACE_IRQFLAGS_SUPPORT is not set.

We could also add that we have:

#
# Minimum requirements an architecture has to meet for us to
# be able to offer generic tracing facilities:
#
config TRACING_SUPPORT
bool
depends on TRACE_IRQFLAGS_SUPPORT
depends on STACKTRACE_SUPPORT
default y

So this can't even be built without TRACE_IRQFLAGS_SUPPORT!

>
> [bigeasy: Commit descrption.]
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> include/linux/trace_events.h | 7 +++----
> kernel/trace/trace_output.c | 2 +-
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -184,8 +184,7 @@ unsigned int tracing_gen_ctx_irq_test(un
>
> enum trace_flag_type {
> TRACE_FLAG_IRQS_OFF = 0x01,
> - TRACE_FLAG_IRQS_NOSUPPORT = 0x02,
> - TRACE_FLAG_NEED_RESCHED = 0x04,
> + TRACE_FLAG_NEED_RESCHED = 0x02,

These flags are user visible (I probably should move them into uapi).
They are parsed by libtraceevent.

Please just remove NOSUPPORT and do not touch NEED_RESCHED.


> TRACE_FLAG_HARDIRQ = 0x08,
> TRACE_FLAG_SOFTIRQ = 0x10,
> TRACE_FLAG_PREEMPT_RESCHED = 0x20,
> @@ -211,11 +210,11 @@ static inline unsigned int tracing_gen_c
>
> static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags)
> {
> - return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
> + return tracing_gen_ctx_irq_test(0);
> }
> static inline unsigned int tracing_gen_ctx(void)
> {
> - return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
> + return tracing_gen_ctx_irq_test(0);
> }
> #endif
>
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -460,7 +460,7 @@ int trace_print_lat_fmt(struct trace_seq
> (entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :
> (entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
> bh_off ? 'b' :
> - (entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
> + !IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' :

Probably can even remove this check.

-- Steve

> '.';
>
> switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |