linux-kernel - Re: [patch 1/2] genirq: Run irq handlers with interrupts disabled

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Date:	Tue, 25 May 2010 13:32:53 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...l.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Venkatesh Pallipadi <venki@...gle.com>
Subject: Re: [patch 1/2] genirq: Run irq handlers with interrupts disabled

Just noticed a minor side effect of this patch on /proc/stat.

As int handlers run with ints disabled, timer interrupt based
samples will no longer account for any irq time. As a result, irq
time in /proc/stat, top, etc will be mostly zero (unless some handler
is enabling ints).

This is not a problem on s390, powerpc, ia64 when VIRT_CPU_ACCOUNTING is
enabled.

May be we should gracefully call it out as zero, with patch like below?

Signed-off-by: Venkatesh Pallipadi <venki@...gle.com>
---
 Documentation/filesystems/proc.txt |    2 +-
 fs/proc/stat.c                     |    4 ++++
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 6507d2a..8f5254a 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1123,7 +1123,7 @@ second).  The meanings of the columns are as follows, from left to right:
 - system: processes executing in kernel mode
 - idle: twiddling thumbs
 - iowait: waiting for I/O to complete
-- irq: servicing interrupts
+- irq: servicing interrupts (valid only with VIRT_CPU_ACCOUNTING, 0 otherwise)
 - softirq: servicing softirqs
 - steal: involuntary wait
 - guest: running a normal guest
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index bf31b03..d92bea8 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -46,7 +46,9 @@ static int show_stat(struct seq_file *p, void *v)
 		idle = cputime64_add(idle, kstat_cpu(i).cpustat.idle);
 		idle = cputime64_add(idle, arch_idle_time(i));
 		iowait = cputime64_add(iowait, kstat_cpu(i).cpustat.iowait);
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
 		irq = cputime64_add(irq, kstat_cpu(i).cpustat.irq);
+#endif
 		softirq = cputime64_add(softirq, kstat_cpu(i).cpustat.softirq);
 		steal = cputime64_add(steal, kstat_cpu(i).cpustat.steal);
 		guest = cputime64_add(guest, kstat_cpu(i).cpustat.guest);
@@ -87,7 +89,9 @@ static int show_stat(struct seq_file *p, void *v)
 		idle = kstat_cpu(i).cpustat.idle;
 		idle = cputime64_add(idle, arch_idle_time(i));
 		iowait = kstat_cpu(i).cpustat.iowait;
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
 		irq = kstat_cpu(i).cpustat.irq;
+#endif
 		softirq = kstat_cpu(i).cpustat.softirq;
 		steal = kstat_cpu(i).cpustat.steal;
 		guest = kstat_cpu(i).cpustat.guest;
-- 
1.7.0.1

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