From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756810Ab0JYXD0 (ORCPT ); Mon, 25 Oct 2010 19:03:26 -0400 Received: from claw.goop.org ([74.207.240.146]:56379 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311Ab0JYXDZ (ORCPT ); Mon, 25 Oct 2010 19:03:25 -0400 Message-ID: <4CC60CB7.3070005@goop.org> Date: Mon, 25 Oct 2010 16:03:19 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.4 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: Ian Campbell , Stefano Stabellini , "H. Peter Anvin" , linux-kernel@vger.kernel.org, mingo@elte.hu, xen-devel@lists.xensource.com, tglx@linutronix.de Subject: Re: [PATCH 1/5] xen: events: use irq_alloc_desc(_at) instead of open-coding an IRQ allocator. References: <1288023736.11153.40.camel@zakaz.uk.xensource.com> <1288023813-31989-1-git-send-email-ian.campbell@citrix.com> <20101025173522.GA5590@dumpdata.com> In-Reply-To: <20101025173522.GA5590@dumpdata.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 On 10/25/2010 10:35 AM, Konrad Rzeszutek Wilk wrote: > On Mon, Oct 25, 2010 at 05:23:29PM +0100, Ian Campbell wrote: >> Encapsulate allocate and free in xen_irq_alloc and xen_irq_free. >> >> Signed-off-by: Ian Campbell >> --- >> drivers/xen/events.c | 68 ++++++++++++++++++++----------------------------- >> 1 files changed, 28 insertions(+), 40 deletions(-) >> >> diff --git a/drivers/xen/events.c b/drivers/xen/events.c >> index 97612f5..c8f3e43 100644 >> --- a/drivers/xen/events.c >> +++ b/drivers/xen/events.c >> @@ -394,41 +394,29 @@ static int find_unbound_pirq(void) >> return -1; >> } >> >> -static int find_unbound_irq(void) >> +static int xen_irq_alloc(void) >> { >> - struct irq_data *data; >> - int irq, res; >> - int start = get_nr_hw_irqs(); >> + int irq = irq_alloc_desc(0); >> >> - if (start == nr_irqs) >> - goto no_irqs; >> - >> - /* nr_irqs is a magic value. Must not use it.*/ >> - for (irq = nr_irqs-1; irq > start; irq--) { >> - data = irq_get_irq_data(irq); >> - /* only 0->15 have init'd desc; handle irq > 16 */ >> - if (!data) >> - break; >> - if (data->chip == &no_irq_chip) >> - break; >> - if (data->chip != &xen_dynamic_chip) >> - continue; >> - if (irq_info[irq].type == IRQT_UNBOUND) >> - return irq; >> - } >> - >> - if (irq == start) >> - goto no_irqs; >> + if (irq < 0) >> + panic("No available IRQ to bind to: increase nr_irqs!\n"); >> >> - res = irq_alloc_desc_at(irq, 0); >> + return irq; >> +} > So I am curious what the /proc/interrupts looks?The issue (and the reason > for this implementation above) was that under PV with PCI devices we would > overlap PCI devices IRQs with Xen event channels. So we could have a USB device > at IRQ 16 _and_ also a xen_spinlock4 handler. That would throw off the system > since the xen_spinlock4 was an edge type handler while the USB device was an > level (at least on my box). What? Why? How? Surely if we're asking the irq subsystem to allocate us an irq, it will return a fresh never-before-used (and certainly not shared) irq? Shared irqs only make sense if multiple devices are actually sharing, say, a wire on the board. Or am I missing something? J