linux-kernel - [PATCH] arm: add stat support to fiq

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Date:   Tue, 29 Nov 2016 23:48:35 +0100
From:   Oussama Ghorbel <ghorbel@...il.com>
To:     Russell King <linux@...linux.org.uk>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Oussama Ghorbel <ghorbel@...il.com>
Subject: [PATCH] arm: add stat support to fiq

This patch allows drivers that uses fiq to have a stat on the
execution number of the fiq handler.
For that three APIs has been defined:
- fiq_kstat_enable: this function enables fiq stat and allocates required
memory for it
- fiq_kstat_disable: this function disable fiq stat and free its allocated
memory
- fiq_kstat_this_cpu_inc: This function increments the fiq stat counter of
the current CPU running the fiq handler

A driver may call fiq_kstat_enable at its initialization to enable fiq
stat and then call fiq_kstat_this_cpu_inc from the fiq handler

When the fiq stat is enabled by a driver, then /proc/interrupts shows the
fiq entry as the following example:
FIQ:          0   21642080          0          0  usb_fiq
If the fiq stat is not enabled, the content will be similar to the old one
as the following example:
FIQ:                                              usb_fiq
The fiq name will be always written on the first column after the last CPU
column

Signed-off-by: Oussama Ghorbel <ghorbel@...il.com>
---
 arch/arm/include/asm/fiq.h | 10 ++++++++++
 arch/arm/kernel/fiq.c      | 31 +++++++++++++++++++++++++++----
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/arch/arm/include/asm/fiq.h b/arch/arm/include/asm/fiq.h
index d493d0b..77f819b 100644
--- a/arch/arm/include/asm/fiq.h
+++ b/arch/arm/include/asm/fiq.h
@@ -31,6 +31,8 @@ struct fiq_handler {
 	/* data for the relinquish/reacquire functions
 	 */
 	void *dev_id;
+	/* fiq stats percpu */
+	unsigned int __percpu *fiq_kstat;
 };
 
 extern int claim_fiq(struct fiq_handler *f);
@@ -53,4 +55,12 @@ static inline void get_fiq_regs(struct pt_regs *regs)
 	__get_fiq_regs(&regs->ARM_r8);
 }
 
+extern int fiq_kstat_enable(struct fiq_handler *fh);
+extern void fiq_kstat_disable(struct fiq_handler *fh);
+
+static inline void fiq_kstat_this_cpu_inc(struct fiq_handler *fh)
+{
+	__this_cpu_inc(*fh->fiq_kstat);
+}
+
 #endif
diff --git a/arch/arm/kernel/fiq.c b/arch/arm/kernel/fiq.c
index 059c3da..4b606df 100644
--- a/arch/arm/kernel/fiq.c
+++ b/arch/arm/kernel/fiq.c
@@ -83,10 +83,19 @@ static struct fiq_handler *current_fiq = &default_owner;
 
 int show_fiq_list(struct seq_file *p, int prec)
 {
-	if (current_fiq != &default_owner)
-		seq_printf(p, "%*s:              %s\n", prec, "FIQ",
-			current_fiq->name);
-
+	int j;
+
+	if (current_fiq == &default_owner)
+		return 0;
+	seq_printf(p, "%*s: ", prec, "FIQ");
+	for_each_online_cpu(j) {
+		if (current_fiq->fiq_kstat)
+			seq_printf(p, "%10u ",
+				*per_cpu_ptr(current_fiq->fiq_kstat, j));
+		else
+			seq_printf(p, "%10s ", "");
+	}
+	seq_printf(p, " %s\n", current_fiq->name);
 	return 0;
 }
 
@@ -162,3 +171,17 @@ void __init init_FIQ(int start)
 	get_fiq_regs(&dfl_fiq_regs);
 	fiq_start = start;
 }
+
+int fiq_kstat_enable(struct fiq_handler *fh)
+{
+	fh->fiq_kstat = alloc_percpu(unsigned int);
+	return fh->fiq_kstat != 0 ? 0 : 1;
+}
+EXPORT_SYMBOL(fiq_kstat_enable);
+
+void fiq_kstat_disable(struct fiq_handler *fh)
+{
+	free_percpu(fh->fiq_kstat);
+	fh->fiq_kstat = NULL;
+}
+EXPORT_SYMBOL(fiq_kstat_disable);
-- 
2.7.4