From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 21 Mar 2011 12:28:03 +1100 From: Anton Blanchard To: paulus@samba.org, benh@kernel.crashing.org Subject: [PATCH] powerpc: Fix accounting of softirq time when idle Message-ID: <20110321122803.114d50c4@kryten> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , commit cf9efce0ce31 (powerpc: Account time using timebase rather than PURR) used in_irq() to detect if the time was spent in interrupt processing. This only catches hardirq context so if we are in softirq context and in the idle loop we end up accounting it as idle time. If we instead use in_interrupt() we catch both softirq and hardirq time. The issue was found when running a network intensive workload. top showed the following: 0.0%us, 1.1%sy, 0.0%ni, 85.7%id, 0.0%wa, 9.9%hi, 3.3%si, 0.0%st 85.7% idle. But this was wildly different to the perf events data. To confirm the suspicion I ran something to keep the core busy: # yes > /dev/null & 8.2%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 10.3%hi, 81.4%si, 0.0%st We only got 8.2% of the CPU for the userspace task and softirq has shot up to 81.4%. With the patch below top shows the correct stats: 0.0%us, 0.0%sy, 0.0%ni, 5.3%id, 0.0%wa, 13.3%hi, 81.3%si, 0.0%st Signed-off-by: Anton Blanchard Cc: stable@kernel.org --- Index: linux-2.6/arch/powerpc/kernel/time.c =================================================================== --- linux-2.6.orig/arch/powerpc/kernel/time.c 2011-03-21 12:05:12.056482258 +1100 +++ linux-2.6/arch/powerpc/kernel/time.c 2011-03-21 12:05:18.516721851 +1100 @@ -356,7 +356,7 @@ void account_system_vtime(struct task_st } get_paca()->user_time_scaled += user_scaled; - if (in_irq() || idle_task(smp_processor_id()) != tsk) { + if (in_interrupt() || idle_task(smp_processor_id()) != tsk) { account_system_time(tsk, 0, delta, sys_scaled); if (stolen) account_steal_time(stolen);