From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965242AbaH0XJZ (ORCPT ); Wed, 27 Aug 2014 19:09:25 -0400 Received: from relay1.sgi.com ([192.48.180.66]:35712 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935728AbaH0XJY (ORCPT ); Wed, 27 Aug 2014 19:09:24 -0400 X-Greylist: delayed 595 seconds by postgrey-1.27 at vger.kernel.org; Wed, 27 Aug 2014 19:09:24 EDT Message-ID: <53FE6515.6050102@sgi.com> Date: Wed, 27 Aug 2014 16:09:09 -0700 From: Mike Travis User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 MIME-Version: 1.0 To: Andrew Morton CC: mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, msalter@redhat.com, dyoung@redhat.com, riel@redhat.com, peterz@infradead.org, mgorman@suse.de, linux-kernel@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, Alex Thorlton Subject: Re: [PATCH 1/2] x86: Optimize resource lookups for ioremap References: <20140827225927.364537333@asylum.americas.sgi.com> <20140827225927.602319674@asylum.americas.sgi.com> <20140827160515.c59f1c191fde5f788a7c42f6@linux-foundation.org> In-Reply-To: <20140827160515.c59f1c191fde5f788a7c42f6@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/27/2014 4:05 PM, Andrew Morton wrote: > On Wed, 27 Aug 2014 17:59:28 -0500 Mike Travis wrote: > >> Since the ioremap operation is verifying that the specified address range >> is NOT RAM, it will search the entire ioresource list if the condition >> is true. To make matters worse, it does this one 4k page at a time. >> For a 128M BAR region this is 32 passes to determine the entire region >> does not contain any RAM addresses. >> >> This patch provides another resource lookup function, region_is_ram, >> that searches for the entire region specified, verifying that it is >> completely contained within the resource region. If it is found, then >> it is checked to be RAM or not, within a single pass. >> >> The return result reflects if it was found or not (-1), and whether it is >> RAM (1) or not (0). This allows the caller to fallback to the previous >> page by page search if it was not found. >> >> ... >> >> --- linux.orig/kernel/resource.c >> +++ linux/kernel/resource.c >> @@ -494,6 +494,43 @@ int __weak page_is_ram(unsigned long pfn >> } >> EXPORT_SYMBOL_GPL(page_is_ram); >> >> +/* >> + * Search for a resouce entry that fully contains the specified region. >> + * If found, return 1 if it is RAM, 0 if not. >> + * If not found, or region is not fully contained, return -1 >> + * >> + * Used by the ioremap functions to insure user not remapping RAM and is as >> + * vast speed up over walking through the resource table page by page. >> + */ >> +int __weak region_is_ram(resource_size_t start, unsigned long size) >> +{ >> + struct resource *p; >> + resource_size_t end = start + size - 1; >> + int flags = IORESOURCE_MEM | IORESOURCE_BUSY; >> + const char *name = "System RAM"; >> + int ret = -1; >> + >> + read_lock(&resource_lock); >> + for (p = iomem_resource.child; p ; p = p->sibling) { >> + if (end < p->start) >> + continue; >> + >> + if (p->start <= start && end <= p->end) { >> + /* resource fully contains region */ >> + if ((p->flags != flags) || strcmp(p->name, name)) >> + ret = 0; >> + else >> + ret = 1; >> + break; >> + } >> + if (p->end < start) >> + break; /* not found */ >> + } >> + read_unlock(&resource_lock); >> + return ret; >> +} >> +EXPORT_SYMBOL_GPL(region_is_ram); > > Exporting a __weak symbol is strange. I guess it works, but neither > the __weak nor the export are actually needed? > I mainly used 'weak' and export because that was what the page_is_ram function was using. Most likely this won't be used anywhere else but I wasn't sure. I can certainly remove the weak and export, at least until it's actually needed?