On 2024-10-22 03:14:18 [-0400], Steven Rostedt wrote:

On Mon, 21 Oct 2024 17:08:40 +0200
Sebastian Andrzej Siewior [off-list ref] wrote:

quoted

From: Thomas Gleixner <redacted>

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!

Good point. So we could TRACE_FLAG_IRQS_NOSUPPORT since it can't be
used. This is since commit 0ea5ee035133a ("tracing: Remove PPC32 wart
from config TRACING_SUPPORT").

quoted

+++ 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.

Then I put the lazy bit where we have not NOSUPPORT.

quoted

 	TRACE_FLAG_HARDIRQ		= 0x08,
 	TRACE_FLAG_SOFTIRQ		= 0x10,
 	TRACE_FLAG_PREEMPT_RESCHED	= 0x20,

--- 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.

Yes.

-- Steve

Sebastian