> -----Original Message----- > From: Russell King - ARM Linux [mailto:linux@xxxxxxxxxxxxxxxx] > Sent: Thursday, December 17, 2009 3:27 PM > To: Hiremath, Vaibhav > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; linux- > omap@xxxxxxxxxxxxxxx > Subject: Re: CPU consumption is going as high as 95% on ARM Cortex > A8 > > 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. > [Hiremath, Vaibhav] Russell, I tried with your suggestion above but unfortunately it didn't work for me. I am seeing the same behavior with the pgprot_dmacoherent(). I pulled your patch (which got applied cleanly on 2.6.32-rc5) - ----------------------------------------- commit 26a26d329688ab018e068b412b03d43d7c299f0a Author: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> Date: Fri Nov 20 21:06:43 2009 +0000 Subject: ARM: dma-mapping: switch ARMv7 DMA mappings to retain 'memory' attribute ----------------------------------------- Any other pointers/suggestions? Thanks, Vaibhav > > 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 from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
