From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 3C3AE6B0087 for ; Thu, 17 Dec 2009 04:56:59 -0500 (EST) Date: Thu, 17 Dec 2009 09:56:41 +0000 From: Russell King - ARM Linux Subject: Re: CPU consumption is going as high as 95% on ARM Cortex A8 Message-ID: <20091217095641.GA399@n2100.arm.linux.org.uk> References: <19F8576C6E063C45BE387C64729E73940449F43857@dbde02.ent.ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <19F8576C6E063C45BE387C64729E73940449F43857@dbde02.ent.ti.com> Sender: owner-linux-mm@kvack.org To: "Hiremath, Vaibhav" Cc: "linux-arm-kernel@lists.infradead.org" , "linux-mm@kvack.org" , "linux-omap@vger.kernel.org" List-ID: On Thu, Dec 17, 2009 at 11:08:31AM +0530, Hiremath, Vaibhav wrote: > Issue/Usage :- > ------------- > The V4l2-Capture driver captures the data from video decoder into buffer > and the application does some processing on this buffer. The mmap > implementation can be found at drivers/media/video/videobuf-dma-contig.c, > function__videobuf_mmap_mapper(). vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); will result in the memory being mapped as 'Strongly Ordered', resulting in there being multiple mappings with differing types. In later kernels, we have pgprot_dmacoherent() and I'd suggest changing the above macro for that. > Without PAGE_READONLY/PAGE_SHARED > > Important bits are [0-9] - 0x383 > > With PAGE_READONLY/PAGE_SHARED set > > Important bits are [0-9] - 0x38F So the difference is the C and B bits, which is more or less expected with the change you've made. > > The lines inside function "cpu_v7_set_pte_ext", is using the flag as shown below - > > tst r1, #L_PTE_USER > orrne r3, r3, #PTE_EXT_AP1 > tstne r3, #PTE_EXT_APX > bicne r3, r3, #PTE_EXT_APX | PTE_EXT_AP0 > > Without PAGE_READONLY/PAGE_SHARED With flags set > > Access perm = reserved Access Perm = Read Only The bits you quote above are L_PTE_* bits, so you need to be careful decoding them. 0x383 gives L_PTE_EXEC|L_PTE_USER|L_PTE_WRITE|L_PTE_YOUNG|L_PTE_PRESENT which is as expected, and will be translated into: APX=0 AP1=1 AP0=0 which is user r/o, system r/w. The same will be true of 0x38f. > - I tried the same thing with another platform (ARM9) and it works fine there. > > Can somebody help me to understand the flag PAGE_SHARED/PAGE_READONLY > and access permissions? Am I debugging this into right path? Does > anybody have seen/observed similar issue before? I think you're just seeing the effects of 'strongly ordered' memory rather than anything actually wrong. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org