linux-kernel - RE: [PATCH 5/6] ACPI/EC: Cleanup QR_SC command processing by adding a kernel thread to poll EC events.

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Date:	Thu, 13 Nov 2014 02:52:03 +0000
From:	"Zheng, Lv" <lv.zheng@...el.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Andi Kleen (ak@...ux.intel.com)" <ak@...ux.intel.com>
Subject: RE: [PATCH 5/6] ACPI/EC: Cleanup QR_SC command processing by adding
 a kernel thread to poll EC events.

Hi, Rafael

> From: Rafael J. Wysocki [mailto:rjw@...ysocki.net]
> Sent: Thursday, November 13, 2014 10:59 AM
> 
> On Thursday, November 13, 2014 02:31:08 AM Zheng, Lv wrote:
> > Hi, Rafael
> >
> > > From: Rafael J. Wysocki [mailto:rjw@...ysocki.net]
> > > Sent: Wednesday, November 12, 2014 9:17 AM
> 
> [cut]
> 
> > > > +
> > > > +static int ec_create_event_poller(struct acpi_ec *ec)
> > > > +{
> > > > +	struct task_struct *t;
> > > > +
> > > > +	t = kthread_run(acpi_ec_event_poller, ec, "ec/gpe-%lu", ec->gpe);
> > >
> > > Does it have to be a kernel thread?
> > >
> > > What about using a workqueue instead?
> >
> > Actually I just want to use threaded IRQ here in response to Andi Kleen's comment.
> > If acpi_irq is registered as threaded IRQ, then acpi_ec_event_poller() will be the
> > callback from it.
> 
> How so?
> 
> > Since ACPICA is not ready for threaded IRQ currently, we cannot proceed at this point.
> > So I copied the threaded IRQ code from kernel/irq/manage.c here to prepare threaded IRQ logics.
> 
> Oh dear, no.
> 
> This isn't the way forward here.
> 
> > Using a separate work queue, we didn't decrease the kernel thread count.
> 
> Why does that matter at all?
> 
> > And the code written for the work item cannot be derived when things are
> > switched to the threaded IRQ.
> > So I used kthread here.
> 
> Please use a workqueue instead.  If/when we need to switch over to threaded
> IRQs, we'll do the work then.  For now, let's not complicate things more
> than necessary.

It seems we need the thread because we will move polling code from ec_poll() to acpi_ec_event_poller().
This will happen right after these cleanups.
That's the threaded IRQ logic - IRQ is polled in the thread.
We cannot achieve this using work queue.

Best regards
-Lv