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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Message-ID: <1586902.iI2oFdt4zk@vostro.rjw.lan>
Date:	Thu, 13 Nov 2014 23:37:41 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"Zheng, Lv" <lv.zheng@...el.com>
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.

On Thursday, November 13, 2014 02:52:03 AM Zheng, Lv wrote:
> 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.

OK

In that case I'm not going to apply this patch, because it is not a cleanup.
It doesn't belong to this series, but to the series that will move the
polling code.

Does patch [6/6] depend on [5/6]?


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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