linux-kernel - Re: Question on handling managed IRQs when hotplugging CPUs

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Message-Id: <20190206133432.GB14106@t480-pf1aa2c2>
Date:   Wed, 6 Feb 2019 14:34:32 +0100
From:   Benjamin Block <bblock@...ux.ibm.com>
To:     John Garry <john.garry@...wei.com>
Cc:     Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Hannes Reinecke <hare@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linuxarm <linuxarm@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hannes Reinecke <hare@...e.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>
Subject: Re: Question on handling managed IRQs when hotplugging CPUs

On Wed, Feb 06, 2019 at 09:21:40AM +0000, John Garry wrote:
> On 05/02/2019 18:23, Christoph Hellwig wrote:
> > On Tue, Feb 05, 2019 at 03:09:28PM +0000, John Garry wrote:
> > > For SCSI devices, unfortunately not all IO sent to the HW originates from
> > > blk-mq or any other single entity.
> > 
> > Where else would SCSI I/O originate from?
> 
> Please note that I was referring to other management IO, like SAS SMP, TMFs,
> and other proprietary commands which the driver may generate for the HBA -
> https://marc.info/?l=linux-scsi&m=154831889001973&w=2 discusses some of them
> also.
> 

Especially the TMFs send via SCSI EH are a bit of a pain I guess,
because they are entirely managed by the device drivers, but depending
on the device driver they might not even qualify for the problem Hannes
is seeing.

-- 
With Best Regards, Benjamin Block      /      Linux on IBM Z Kernel Development
IBM Systems & Technology Group   /  IBM Deutschland Research & Development GmbH
Vorsitz. AufsR.: Matthias Hartmann       /      Geschäftsführung: Dirk Wittkopp
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