linux-kernel - Re: 100% iowait on one of cpus in current -git

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Date:	Mon, 22 Oct 2007 12:40:24 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Fengguang Wu <fengguang.wu@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 100% iowait on one of cpus in current -git

On Monday 22 October 2007 12:22:10 Peter Zijlstra wrote:
> On Mon, 2007-10-22 at 11:59 +0200, Maxim Levitsky wrote:
> > On Monday 22 October 2007 11:41:57 Peter Zijlstra wrote:
> > > On Mon, 2007-10-22 at 08:22 +0200, Maxim Levitsky wrote:
> > > > Hi,
> > > > 
> > > > I found a bug in current -git:
> > > > 
> > > > On my system on of cpus stays 100% in iowait mode (I have core 2 duo)
> > > > Otherwise the system works OK, no disk activity and/or slowdown.
> > > > Suspecting that this is a swap-related problem I tried to turn swap of, but it doesn't affect anything.
> > > > It is probably some accounting bug.
> > > > 
> > > > If I start with init=/bin/bash, then this disappears.
> > > > I tried then to start usual /etc/init.d scripts then, and first one to show this bug was gpm.
> > > > but then I rebooted the system to X without gpm, and I still see 100% iowait.
> > > > 
> > > > No additional messages in dmesg.
> > > 
> > > does sysrq-t show any D state tasks?
> > > 
> > > 
> > This one:
> > Probably per-block device dirty writeback?
> > I am compiling now revision 1f7d6668c29b1dfa307a44844f9bb38356fc989b
> > Thanks for the pointer.
> > 
> > 
> > 
> > [  673.365631] pdflush       D c21bdecc     0   221      2
> > [  673.365635]        c21bdee0 00000046 00000002 c21bdecc c21bdec4 00000000 c21b3000 00000002
> > [  673.365643]        c0134892 c21b3164 c1e00200 00000001 c7109280 c21bdec0 c03ff849 c21bdef0
> > [  673.365650]        00052974 00000000 000000ff 00000000 00000000 00000000 c21bdef0 000529dc
> > [  673.365657] Call Trace:
> > [  673.365659]  [<c03fd728>] schedule_timeout+0x48/0xc0
> > [  673.365663]  [<c03fd50e>] io_schedule_timeout+0x5e/0xb0
> > [  673.365667]  [<c0170d11>] congestion_wait+0x71/0x90
> > [  673.365671]  [<c016b92e>] wb_kupdate+0x9e/0xf0
> > [  673.365675]  [<c016beb2>] pdflush+0x102/0x1d0
> > [  673.365679]  [<c013fa82>] kthread+0x42/0x70
> > [  673.365683]  [<c01050df>] kernel_thread_helper+0x7/0x18
> > 
> 
> That looks more like the inode writeback patches from Wu than the per
> bdi dirty stuff. The later typically hangs in balance_dirty_pages().
> 
> 
> 

Yes, you are right,

both revisions 1f7d6668c29b1dfa307a44844f9bb38356fc989b and 3e26c149c358529b1605f8959341d34bc4b880a3 work fine
But I didn't pay attention that those are before f4a1c2bce002f683801bcdbbc9fd89804614fb6b.
So, back to the drawing board.... :-)

Will test revision 2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b, just after writeback patches.
Thanks,
	Best regards,
		Maxim Levitsky
		
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