From: John Garry <john.garry@huawei.com>
To: Hannes Reinecke <hare@suse.de>, Thomas Gleixner <tglx@linutronix.de>
Cc: Keith Busch <keith.busch@intel.com>,
Christoph Hellwig <hch@lst.de>,
"Marc Zyngier" <marc.zyngier@arm.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"Peter Zijlstra" <peterz@infradead.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Linuxarm <linuxarm@huawei.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Hannes Reinecke <hare@suse.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: Question on handling managed IRQs when hotplugging CPUs
Date: Tue, 5 Feb 2019 13:24:11 +0000 [thread overview]
Message-ID: <42d149c5-0380-c357-8811-81015159ac04@huawei.com> (raw)
In-Reply-To: <d93ff049-e96d-36ce-7e58-ec97cbb27ed0@suse.de>
On 04/02/2019 07:12, Hannes Reinecke wrote:
> On 2/1/19 10:57 PM, Thomas Gleixner wrote:
>> On Fri, 1 Feb 2019, Hannes Reinecke wrote:
>>> Thing is, if we have _managed_ CPU hotplug (ie if the hardware
>>> provides some
>>> means of quiescing the CPU before hotplug) then the whole thing is
>>> trivial;
>>> disable SQ and wait for all outstanding commands to complete.
>>> Then trivially all requests are completed and the issue is resolved.
>>> Even with todays infrastructure.
>>>
>>> And I'm not sure if we can handle surprise CPU hotplug at all, given
>>> all the
>>> possible race conditions.
>>> But then I might be wrong.
>>
>> The kernel would completely fall apart when a CPU would vanish by
>> surprise,
>> i.e. uncontrolled by the kernel. Then the SCSI driver exploding would be
>> the least of our problems.
>>
> Hehe. As I thought.
Hi Hannes,
>
> So, as the user then has to wait for the system to declars 'ready for
> CPU remove', why can't we just disable the SQ and wait for all I/O to
> complete?
> We can make it more fine-grained by just waiting on all outstanding I/O
> on that SQ to complete, but waiting for all I/O should be good as an
> initial try.
> With that we wouldn't need to fiddle with driver internals, and could
> make it pretty generic.
I don't fully understand this idea - specifically, at which layer would
we be waiting for all the IO to complete?
> And we could always add more detailed logic if the driver has the means
> for doing so.
>
Thanks,
John
> Cheers,
>
> Hannes
next prev parent reply other threads:[~2019-02-05 13:24 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <f6f6e031-8b79-439d-c2af-8d3e76f30710@huawei.com>
[not found] ` <20190129154433.GF15302@localhost.localdomain>
[not found] ` <757902fc-a9ea-090b-7853-89944a0ce1b5@huawei.com>
[not found] ` <20190129172059.GC17132@localhost.localdomain>
[not found] ` <3fe63dab-0791-f476-69c4-9866b70e8520@huawei.com>
[not found] ` <alpine.DEB.2.21.1901301338170.5537@nanos.tec.linutronix.de>
2019-01-31 17:48 ` Question on handling managed IRQs when hotplugging CPUs John Garry
2019-02-01 15:56 ` Hannes Reinecke
2019-02-01 21:57 ` Thomas Gleixner
2019-02-04 7:12 ` Hannes Reinecke
2019-02-05 13:24 ` John Garry [this message]
2019-02-05 14:52 ` Keith Busch
2019-02-05 15:09 ` John Garry
2019-02-05 15:11 ` Keith Busch
2019-02-05 15:15 ` Hannes Reinecke
2019-02-05 15:27 ` John Garry
2019-02-05 18:23 ` Christoph Hellwig
2019-02-06 9:21 ` John Garry
2019-02-06 13:34 ` Benjamin Block
2019-02-05 15:10 ` Hannes Reinecke
2019-02-05 15:16 ` Keith Busch
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