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: <1961414.bGx3EdA0yT@vostro.rjw.lan>
Date:	Thu, 13 Nov 2014 03:58:39 +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 02:31:08 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.

Rafael

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