From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH 5/6] ACPI/EC: Cleanup QR_SC command processing by adding a kernel thread to poll EC events. Date: Sat, 15 Nov 2014 00:38:14 +0100 Message-ID: <3572803.mV1m1IsC13@vostro.rjw.lan> References: <1586902.iI2oFdt4zk@vostro.rjw.lan> <1AE640813FDE7649BE1B193DEA596E88026A0A0F@SHSMSX101.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: Received: from v094114.home.net.pl ([79.96.170.134]:59627 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S933574AbaKNXRP (ORCPT ); Fri, 14 Nov 2014 18:17:15 -0500 In-Reply-To: <1AE640813FDE7649BE1B193DEA596E88026A0A0F@SHSMSX101.ccr.corp.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Zheng, Lv" Cc: "Wysocki, Rafael J" , "Brown, Len" , Lv Zheng , "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "Andi Kleen (ak@linux.intel.com)" On Friday, November 14, 2014 01:21:51 AM Zheng, Lv wrote: > Hi, Rafael > > > From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net] > > Sent: Friday, November 14, 2014 6:38 AM > > > > On Thursday, November 13, 2014 02:52:03 AM Zheng, Lv wrote: > > > Hi, Rafael > > > > > > > From: Rafael J. Wysocki [mailto:rjw@rjwysocki.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@rjwysocki.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. > > If we'll defer some execution and we know there will only be one execution corresponding to one indication, work item can fit. > If we'll poll something or there is no such 1 to 1 correspondence, using work queue may accumulate useless work items. > > We have the work item to evaluate _Qxx in the EC driver, for the IRQ indications, IMO, it's better to use an IRQ poller thread. > And it's easier for me to control future improvements using kthread: > 1. We need the SCI_EVT draining support for Samsung firmware. For Samsung, 1 SCI_EVT indication may mean several QR_EC transactions as we cannot rely on SCI_EVT value, it can be cleared by Samsung firmware before 0x00 is returned. > 2. For Acer firmware, firmware will refuse to respond QR_EC if SCI_EVT=0 and further transactions will be blocked. Whether a transaction abort support is needed is unclear to me now because I'm not sure if this will appear on other platforms. When supporting this, I may face the difficulty to abort several queued up work items but for IRQ poller thread, I only need to abort the very 1 query transaction. > > > Does patch [6/6] depend on [5/6]? > > Patch [6/6] depends on [5/6]. > So you can just take the patch 1-4 first.. > I'll ask Samsung users to test an improved event draining support based on the poller thread and re-send the patch [5/5] and patch [6/6] after that. OK So patches [1-4/6] queued up for 3.19, thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.