From: Toshi Kani <toshi.kani@hp.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: linux-s390@vger.kernel.org, jiang.liu@huawei.com,
wency@cn.fujitsu.com, linux-acpi@vger.kernel.org,
Greg KH <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
isimatu.yasuaki@jp.fujitsu.com, yinghai@kernel.org,
srivatsa.bhat@linux.vnet.ibm.com, guohanjun@huawei.com,
bhelgaas@google.com, akpm@linux-foundation.org,
linuxppc-dev@lists.ozlabs.org, lenb@kernel.org
Subject: Re: [RFC PATCH v2 01/12] Add sys_hotplug.h for system device hotplug framework
Date: Mon, 04 Feb 2013 13:34:18 -0700 [thread overview]
Message-ID: <1360010058.23410.169.camel@misato.fc.hp.com> (raw)
In-Reply-To: <23473445.t1DSaBm58X@vostro.rjw.lan>
On Mon, 2013-02-04 at 21:12 +0100, Rafael J. Wysocki wrote:
> On Monday, February 04, 2013 12:46:24 PM Toshi Kani wrote:
> > On Mon, 2013-02-04 at 20:48 +0100, Rafael J. Wysocki wrote:
> > > On Monday, February 04, 2013 09:02:46 AM Toshi Kani wrote:
> > > > On Mon, 2013-02-04 at 14:41 +0100, Rafael J. Wysocki wrote:
> > > > > On Sunday, February 03, 2013 07:23:49 PM Greg KH wrote:
> > > > > > On Sat, Feb 02, 2013 at 09:15:37PM +0100, Rafael J. Wysocki wrote:
> > > > > > > On Saturday, February 02, 2013 03:58:01 PM Greg KH wrote:
> > > > :
> > > > > > > Yes, but those are just remove events and we can only see how destructive they
> > > > > > > were after the removal. The point is to be able to figure out whether or not
> > > > > > > we *want* to do the removal in the first place.
> > > > > >
> > > > > > Yes, but, you will always race if you try to test to see if you can shut
> > > > > > down a device and then trying to do it. So walking the bus ahead of
> > > > > > time isn't a good idea.
> > > > > >
> > > > > > And, we really don't have a viable way to recover if disconnect() fails,
> > > > > > do we. What do we do in that situation, restore the other devices we
> > > > > > disconnected successfully? How do we remember/know what they were?
> > > > > >
> > > > > > PCI hotplug almost had this same problem until the designers finally
> > > > > > realized that they just had to accept the fact that removing a PCI
> > > > > > device could either happen by:
> > > > > > - a user yanking out the device, at which time the OS better
> > > > > > clean up properly no matter what happens
> > > > > > - the user asked nicely to remove a device, and the OS can take
> > > > > > as long as it wants to complete that action, including
> > > > > > stalling for noticable amounts of time before eventually,
> > > > > > always letting the action succeed.
> > > > > >
> > > > > > I think the second thing is what you have to do here. If a user tells
> > > > > > the OS it wants to remove these devices, you better do it. If you
> > > > > > can't, because memory is being used by someone else, either move them
> > > > > > off, or just hope that nothing bad happens, before the user gets
> > > > > > frustrated and yanks out the CPU/memory module themselves physically :)
> > > > >
> > > > > Well, that we can't help, but sometimes users really *want* the OS to tell them
> > > > > if it is safe to unplug something at this particualr time (think about the
> > > > > Windows' "safe remove" feature for USB sticks, for example; that came out of
> > > > > users' demand AFAIR).
> > > > >
> > > > > So in my opinion it would be good to give them an option to do "safe eject" or
> > > > > "forcible eject", whichever they prefer.
> > > >
> > > > For system device hot-plug, it always needs to be "safe eject". This
> > > > feature will be implemented on mission critical servers, which are
> > > > managed by professional IT folks. Crashing a server causes serious
> > > > money to the business.
> > >
> > > Well, "always" is a bit too strong a word as far as human behavior is concerned
> > > in my opinion.
> > >
> > > That said I would be perfectly fine with not supporting the "forcible eject" to
> > > start with and waiting for the first request to add support for it. I also
> > > would be fine with taking bets on how much time it's going to take for such a
> > > request to appear. :-)
> >
> > Sounds good. In my experience, though, it actually takes a LONG time to
> > convince customers that "safe eject" is actually safe. Enterprise
> > customers are so afraid of doing anything risky that might cause the
> > system to crash or hang due to some defect. I would be very surprised
> > to see a customer asking for a force operation when we do not guarantee
> > its outcome. I have not seen such enterprise customers yet.
>
> But we're talking about a kernel that is supposed to run on mobile phones too,
> among other things.
I think using this feature for RAS i.e. replacing a faulty device
on-line, will continue to be limited for high-end systems. For low-end
systems, it does not make sense for customers to pay much $$ for this
feature. They can just shut the system down for replacement, or they
can simply buy a new system instead of repairing.
That said, using this feature on VM for workload balancing does not
require any special hardware. So, I can see someone willing to try out
to see how it goes with a force option on VM for personal use.
Thanks,
-Toshi
next prev parent reply other threads:[~2013-02-04 20:44 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-10 23:40 [RFC PATCH v2 00/12] System device hot-plug framework Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 01/12] Add sys_hotplug.h for system device hotplug framework Toshi Kani
2013-01-11 21:23 ` Rafael J. Wysocki
2013-01-14 15:33 ` Toshi Kani
2013-01-14 18:48 ` Rafael J. Wysocki
2013-01-14 19:02 ` Toshi Kani
2013-01-30 4:48 ` Greg KH
2013-01-31 1:15 ` Toshi Kani
2013-01-31 5:24 ` Greg KH
2013-01-31 14:42 ` Toshi Kani
2013-01-30 4:53 ` Greg KH
2013-01-31 1:46 ` Toshi Kani
2013-01-30 4:58 ` Greg KH
2013-01-31 2:57 ` Toshi Kani
2013-01-31 20:54 ` Rafael J. Wysocki
2013-02-01 1:32 ` Toshi Kani
2013-02-01 7:30 ` Greg KH
2013-02-01 20:40 ` Toshi Kani
2013-02-01 22:21 ` Rafael J. Wysocki
2013-02-01 23:12 ` Toshi Kani
2013-02-02 15:01 ` Greg KH
2013-02-04 0:28 ` Toshi Kani
2013-02-04 12:46 ` Greg KH
2013-02-04 16:46 ` Toshi Kani
2013-02-04 19:45 ` Rafael J. Wysocki
2013-02-04 20:59 ` Toshi Kani
2013-02-04 23:23 ` Rafael J. Wysocki
2013-02-04 23:33 ` Toshi Kani
2013-02-01 7:23 ` Greg KH
2013-02-01 22:12 ` Rafael J. Wysocki
2013-02-02 14:58 ` Greg KH
2013-02-02 20:15 ` Rafael J. Wysocki
2013-02-02 22:18 ` [PATCH?] Move ACPI device nodes under /sys/firmware/acpi (was: Re: [RFC PATCH v2 01/12] Add sys_hotplug.h for system device hotplug framework) Rafael J. Wysocki
2013-02-04 1:24 ` Greg KH
2013-02-04 12:34 ` Rafael J. Wysocki
2013-02-03 20:44 ` [RFC PATCH v2 01/12] Add sys_hotplug.h for system device hotplug framework Rafael J. Wysocki
2013-02-04 12:48 ` Greg KH
2013-02-04 14:21 ` Rafael J. Wysocki
2013-02-04 14:33 ` Greg KH
2013-02-04 20:07 ` Rafael J. Wysocki
2013-02-04 22:13 ` Toshi Kani
2013-02-04 23:52 ` Rafael J. Wysocki
2013-02-05 0:04 ` Greg KH
2013-02-05 1:02 ` Rafael J. Wysocki
2013-02-05 11:11 ` Rafael J. Wysocki
2013-02-05 18:39 ` Greg KH
2013-02-05 21:13 ` Rafael J. Wysocki
2013-02-05 0:55 ` Toshi Kani
2013-02-04 16:19 ` Toshi Kani
2013-02-04 19:43 ` Rafael J. Wysocki
2013-02-04 1:23 ` Greg KH
2013-02-04 13:41 ` Rafael J. Wysocki
2013-02-04 16:02 ` Toshi Kani
2013-02-04 19:48 ` Rafael J. Wysocki
2013-02-04 19:46 ` Toshi Kani
2013-02-04 20:12 ` Rafael J. Wysocki
2013-02-04 20:34 ` Toshi Kani [this message]
2013-02-04 23:19 ` Rafael J. Wysocki
2013-01-10 23:40 ` [RFC PATCH v2 02/12] ACPI: " Toshi Kani
2013-01-11 21:25 ` Rafael J. Wysocki
2013-01-14 15:53 ` Toshi Kani
2013-01-14 18:47 ` Rafael J. Wysocki
2013-01-14 18:42 ` Toshi Kani
2013-01-14 19:07 ` Rafael J. Wysocki
2013-01-14 19:21 ` Toshi Kani
2013-01-30 4:51 ` Greg KH
2013-01-31 1:38 ` Toshi Kani
2013-01-14 19:21 ` Greg KH
2013-01-14 19:29 ` Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 03/12] drivers/base: Add " Toshi Kani
2013-01-30 4:54 ` Greg KH
2013-01-31 1:48 ` Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 04/12] cpu: Add cpu hotplug handlers Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 05/12] mm: Add memory " Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 06/12] ACPI: Add ACPI bus " Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 07/12] ACPI: Add ACPI resource hotplug handler Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 08/12] ACPI: Update processor driver for hotplug framework Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 09/12] ACPI: Update memory " Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 10/12] ACPI: Update container " Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 11/12] cpu: Update sysfs cpu/online " Toshi Kani
2013-01-10 23:40 ` [RFC PATCH v2 12/12] ACPI: Update sysfs eject " Toshi Kani
2013-01-17 0:50 ` [RFC PATCH v2 00/12] System device hot-plug framework Rafael J. Wysocki
2013-01-17 17:59 ` Toshi Kani
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