From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757672Ab0ERVxA (ORCPT ); Tue, 18 May 2010 17:53:00 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:58738 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755610Ab0ERVw5 (ORCPT ); Tue, 18 May 2010 17:52:57 -0400 Message-ID: <4BF30C32.1020403@linux.vnet.ibm.com> Date: Tue, 18 May 2010 16:52:50 -0500 From: Brian King User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.9) Gecko/20100317 SUSE/3.0.4-1.1.1 Thunderbird/3.0.4 MIME-Version: 1.0 To: dvhltc@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, Will Schmidt , Thomas Gleixner , Jan-Bernd Themann , niv@linux.vnet.ibm.com, Michael Ellerman , Doug Maxey , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY) References: <4BF30793.5070300@us.ibm.com> In-Reply-To: <4BF30793.5070300@us.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Is IRQF_NODELAY something specific to the RT kernel? I don't see it in mainline... -Brian On 05/18/2010 04:33 PM, dvhltc@linux.vnet.ibm.com wrote: >>>From ad81664794e33d785f533c5edee37aaba20dd92d Mon Sep 17 00:00:00 2001 > From: Darren Hart > Date: Tue, 18 May 2010 11:07:13 -0700 > Subject: [PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY) > > The underlying hardware is edge triggered but presented by XICS as level > triggered. The edge triggered interrupts are not reissued after masking. This > is not a problem in mainline which does not mask the interrupt (relying on the > EOI mechanism instead). The threaded interrupts in PREEMPT_RT do mask the > interrupt, and can lose interrupts that occurred while masked, resulting in a > hung ethernet interface. > > The receive handler simply calls napi_schedule(), as such, there is no > significant additional overhead in making this non-threaded, since we either > wakeup the threaded irq handler to call napi_schedule(), or just call > napi_schedule() directly to wakeup the softirqs. As the receive handler is > lockless, there is no need to convert any of the ehea spinlock_t's to > atomic_spinlock_t's. > > Without this patch, a simple scp file copy loop would fail quickly (usually > seconds). We have over two hours of sustained scp activity with the patch > applied. > > Credit goes to Will Schmidt for lots of instrumentation and tracing which > clarified the scenario and to Thomas Gleixner for the incredibly simple > solution. > > Signed-off-by: Darren Hart > Acked-by: Will Schmidt > Cc: Thomas Gleixner > Cc: Jan-Bernd Themann > Cc: Nivedita Singhvi > Cc: Brian King > Cc: Michael Ellerman > Cc: Doug Maxey > --- > drivers/net/ehea/ehea_main.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/net/ehea/ehea_main.c b/drivers/net/ehea/ehea_main.c > index 977c3d3..2c53df2 100644 > --- a/drivers/net/ehea/ehea_main.c > +++ b/drivers/net/ehea/ehea_main.c > @@ -1263,7 +1263,7 @@ static int ehea_reg_interrupts(struct net_device *dev) > "%s-queue%d", dev->name, i); > ret = ibmebus_request_irq(pr->eq->attr.ist1, > ehea_recv_irq_handler, > - IRQF_DISABLED, pr->int_send_name, > + IRQF_DISABLED | IRQF_NODELAY, pr->int_send_name, > pr); > if (ret) { > ehea_error("failed registering irq for ehea_queue " -- Brian King Linux on Power Virtualization IBM Linux Technology Center