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From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Wanpeng Li <kernellwp@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Tariq Toukan <tariqt@mellanox.com>,
	Tariq Toukan <ttoukan.linux@gmail.com>,
	Rik van Riel <riel@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	brouer@redhat.com
Subject: Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28
Date: Tue, 28 Mar 2017 15:18:54 +0200	[thread overview]
Message-ID: <20170328151854.5c50dbd4@redhat.com> (raw)
In-Reply-To: <20170328130602.GA4216@lerouge>

On Tue, 28 Mar 2017 15:06:04 +0200
Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Tue, Mar 28, 2017 at 02:26:42PM +0200, Peter Zijlstra wrote:
> > On Tue, Mar 28, 2017 at 06:34:52PM +0800, Wanpeng Li wrote:  
> > > 
> > > sched_clock_cpu(cpu) should be converted from cputime to ns.  
> > 
> > Uhm, no. sched_clock_cpu() returns u64 in ns.  
> 
> Yes, and most of the cputime_t have been converted to u64 so there
> should be no such conversion issue between u64 and cputime_t anymore.
> 
> Perhaps my commit has another side effect on softirq time accounting,
> I'll see if I can reproduce.

(Disclaimer without knowing anything about the scheduler code)
my theory is that irqtime_account_irq() does not get invoked often
enough, as in my pktgen "overload" use-case keeps softirq always
running. And your change moved updating cpustat[CPUTIME_SOFTIRQ] here.
Before it got updated by account_other_time() which gets invoked from
irqtime_account_process_tick().

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

WARNING: multiple messages have this Message-ID (diff)
From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Wanpeng Li <kernellwp@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Tariq Toukan <tariqt@mellanox.com>,
	Tariq Toukan <ttoukan.linux@gmail.com>,
	Rik van Riel <riel@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	brouer@redhat.com
Subject: Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28
Date: Tue, 28 Mar 2017 15:18:54 +0200	[thread overview]
Message-ID: <20170328151854.5c50dbd4@redhat.com> (raw)
In-Reply-To: <20170328130602.GA4216@lerouge>

On Tue, 28 Mar 2017 15:06:04 +0200
Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Tue, Mar 28, 2017 at 02:26:42PM +0200, Peter Zijlstra wrote:
> > On Tue, Mar 28, 2017 at 06:34:52PM +0800, Wanpeng Li wrote:  
> > > 
> > > sched_clock_cpu(cpu) should be converted from cputime to ns.  
> > 
> > Uhm, no. sched_clock_cpu() returns u64 in ns.  
> 
> Yes, and most of the cputime_t have been converted to u64 so there
> should be no such conversion issue between u64 and cputime_t anymore.
> 
> Perhaps my commit has another side effect on softirq time accounting,
> I'll see if I can reproduce.

(Disclaimer without knowing anything about the scheduler code)
my theory is that irqtime_account_irq() does not get invoked often
enough, as in my pktgen "overload" use-case keeps softirq always
running. And your change moved updating cpustat[CPUTIME_SOFTIRQ] here.
Before it got updated by account_other_time() which gets invoked from
irqtime_account_process_tick().

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

--
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  reply	other threads:[~2017-03-28 13:19 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-28  8:14 Bisected softirq accounting issue in v4.11-rc1~170^2~28 Jesper Dangaard Brouer
2017-03-28  8:14 ` Jesper Dangaard Brouer
2017-03-28 10:34 ` Wanpeng Li
2017-03-28 10:34   ` Wanpeng Li
2017-03-28 11:49   ` Jesper Dangaard Brouer
2017-03-28 11:49     ` Jesper Dangaard Brouer
2017-03-28 12:26   ` Peter Zijlstra
2017-03-28 12:26     ` Peter Zijlstra
2017-03-28 13:06     ` Frederic Weisbecker
2017-03-28 13:06       ` Frederic Weisbecker
2017-03-28 13:18       ` Jesper Dangaard Brouer [this message]
2017-03-28 13:18         ` Jesper Dangaard Brouer
2017-03-28 14:34 ` Frederic Weisbecker
2017-03-28 14:34   ` Frederic Weisbecker
2017-03-28 15:23   ` Jesper Dangaard Brouer
2017-03-28 15:23     ` Jesper Dangaard Brouer
2017-03-28 21:11     ` Frederic Weisbecker
2017-03-28 21:11       ` Frederic Weisbecker
2017-03-28 21:11       ` Frederic Weisbecker
2017-03-29  9:30       ` Jesper Dangaard Brouer
2017-03-29  9:30         ` Jesper Dangaard Brouer
2017-03-29 13:13         ` Frederic Weisbecker
2017-03-29 13:13           ` Frederic Weisbecker
2017-03-29 13:13           ` Frederic Weisbecker

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