linux-kernel - Re: CPU hotplug broken with 2GB VMSPLIT

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Date:	Fri, 1 Dec 2006 08:12:40 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Nathan Lynch <ntl@...ox.com>, linux-kernel@...r.kernel.org,
	akpm@...l.org, pavel@....cz, bryce@...l.org,
	Zwane Mwaikambo <zwane@....linux.org.uk>
Subject: Re: CPU hotplug broken with 2GB VMSPLIT

On Fri, Dec 01 2006, Shaohua Li wrote:
> On Fri, 2006-12-01 at 01:20 +0800, Nathan Lynch wrote:
> > Nathan Lynch wrote:
> > > Jens Axboe wrote:
> > > > On Thu, Nov 30 2006, Jens Axboe wrote:
> > > > > Hi,
> > > > >
> > > > > Just got a new notebook (Lenovo X60), setup a custom kernel and
> > then I
> > > > > noticed that suspend to ram doesn't work anymore. The machine
> > suspends
> > > > > just fine, on resume it brings back the text display but reboots
> > after
> > > > > it has stalled for a few seconds. On the suggestion of Pavel, I
> > tried
> > > > > testing CPU hotplug, and indeed he was right: I can offline 1 of
> > the
> > > > > cores fine, bringing it back online freezes the machine for 3-4
> > seconds
> > > > > and then reboots.
> > > > >
> > > > > carl:/sys/devices/system/cpu/cpu1 # echo 0 > online
> > > > > carl:/sys/devices/system/cpu/cpu1 # dmesg
> > > > > Breaking affinity for irq 219
> > > > > CPU 1 is now offline
> > > > > SMP alternatives: switching to UP code
> > > > > carl:/sys/devices/system/cpu/cpu1 # echo 1 > online
> > > > > Read from remote host carl: Connection reset by peer
> > > > >
> > > > > Booting with maxcpus=1 and resume works fine. Does this ring a
> > bell with
> > > > > anyone? With highmem enabled and the standard vmsplit, cpu
> > hotplug works
> > > > > fine for me.
> > > >
> > > > Some more clues - booting with noreplacement doesn't fix it, so I
> > think
> > > > the alternatives code is off the hook.
> > >
> > > I don't think this adds any new information, but it has been open
> > > awhile:
> > >
> > > http://bugme.osdl.org/show_bug.cgi?id=6542
> > >
> > > I was able to narrow it down to the vmsplit setting but I wasn't
> > able
> > > to debug it further.
> > 
> > Hmm, I'm pretty sure this is the same problem I reported in March,
> > there might be some more information in that thread:
> > 
> > http://marc.theaimsgroup.com/?t=114039363100002&r=1&w=1
> > 
> > but I didn't realize it was vmsplit-related at that time.
> Does this patch help?

It does! Booted a vmsplit 2G kernel again, and started with offlining
and onlining CPU1. Worked fine, that would previously reboot the
notebook. Then I did a suspend-to-ram -> resume cycle, worked fine as
well. Thanks!

-- 
Jens Axboe

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