Messages in this thread Patch in this message | | | Date | Thu, 13 Mar 2014 15:34:49 +0800 | From | Liu hua <> | Subject | Re: [ARM]Fixmap mapping region is not enough for system of 14+ CPUs. |
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On 2014/3/13 1:08, Nicolas Pitre wrote: > On Wed, 12 Mar 2014, Liu hua wrote: > >> Hi Russell, Will or Nicolas, >> >> (In this mail, we only discuss ARM 32-bit linux.) >> >> As we know, the region (0xfff00000-0xfffdffff) is reserved as fixmap >> mapping region. >> >> The function "kmap_atomic" maps highmem pages to this region referring >> to CPUID and per-cpu variable "__kmap_atomic_idx" via >> >> idx = type + KM_TYPE_NR * smp_processor_id(); >> vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx); >> >> Size of region used by one cpu is 0x10000 (KM_TYPE_NR << PAGE_SHIFT). >> And the total size of the fixmap mapping region is 0xe0000. >> (only support 14 CPUs). >> >> So in a system of more than 14 CPUs, this region is not large enough. >> should we change the memory layout on ARM Linux to support 14+ cpu system ? >> Or can we do anything else to support that ? > > How many CPUs do you have? > > What about the following patch? If this doesn't work for you then more > intrusive changes will be needed. > > diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h > index 68ea615c2a..254f2df08d 100644 > --- a/arch/arm/include/asm/fixmap.h > +++ b/arch/arm/include/asm/fixmap.h > @@ -14,7 +14,17 @@ > */ > > #define FIXADDR_START 0xfff00000UL > + > +#if !defined(CONFIG_HAVE_TCM) && !defined(CONFIG_CPU_XSCALE) > +/* > + * If no TCM nor on on a XScale then enlarge the fixmap area to > + * accommodate up to 30 CPUs. > + */ > +#define FIXADDR_END 0xffff0000UL > +#else > #define FIXADDR_END 0xfffe0000UL One cpu need 0x10000-size region; So this patch can only support uo to 15 CPUs > +#endif > + > #define FIXADDR_TOP (FIXADDR_END - PAGE_SIZE) > > enum fixed_addresses { > > > Nicolas >
We have 16 CPUs in our system. And your patch cannot work if the CPU number exceeds 15.
In addition, we can configure NR_CPUS up to 32. So should we solve this problem completely?
There is an 1M-size hole between DMA mapping region and fixmap mapping region(0xffe00000-0xfff00000).if this region are belonged to fixmap mapping region, it can only support 30 CPUs.
Since we have alloced a second level page table to coverring 0xffe00000 - 0xffffffff(2M). And 0xffff0000 upwards used as vector pages. So if the left region is all used as fixmap mapping region(size : 0x1f0000). Up to 31 CPUs is supported.
The following patch can solve our problem(up to 30 CPUs), But it reduce the DMA region. What do you think about it ? Is is necessory to solve this problem completely(up to 32 CPUs) ?
Liu Hua
----------------- diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h index 68ea615..8379891 100644 --- a/arch/arm/include/asm/fixmap.h +++ b/arch/arm/include/asm/fixmap.h @@ -13,7 +13,7 @@ * 0xfffe0000 and 0xfffeffff. */
-#define FIXADDR_START 0xfff00000UL +#define FIXADDR_START 0xffe00000UL #define FIXADDR_END 0xfffe0000UL #define FIXADDR_TOP (FIXADDR_END - PAGE_SIZE)
diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h index 4afb376..0c40674 100644 --- a/arch/arm/include/asm/memory.h +++ b/arch/arm/include/asm/memory.h @@ -83,7 +83,7 @@ */ #define IOREMAP_MAX_ORDER 24
-#define CONSISTENT_END (0xffe00000UL) +#define CONSISTENT_END (0xffd00000UL)
#else /* CONFIG_MMU */
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