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Date: Wed, 14 Oct 2015 00:00:02 +0900 From: Jungseok Lee <jungseoklee85@...il.com> To: James Morse <james.morse@....com> Cc: takahiro.akashi@...aro.org, catalin.marinas@....com, will.deacon@....com, linux-arm-kernel@...ts.infradead.org, mark.rutland@....com, barami97@...il.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH v4 2/2] arm64: Expand the stack trace feature to support IRQ stack On Oct 13, 2015, at 8:00 PM, James Morse wrote: > Hi Jungseok, Hi James, > On 12/10/15 23:13, Jungseok Lee wrote: >> On Oct 13, 2015, at 1:34 AM, James Morse wrote: >>> Having two kmem_caches for 16K stacks on a 64K page system may be wasteful >>> (especially for systems with few cpus)… >> >> This would be a single concern. To address this issue, I drop the 'static' >> keyword in thread_info_cache. Please refer to the below hunk. > > Its only a problem on systems with 64K pages, which don't have a multiple > of 4 cpus. I suspect if you turn on 64K pages, you have many cores with > plenty of memory… Yes, the problem 'two kmem_caches' comes from only 64K page system. I don't get the statement 'which don't have a multiple of 4 cpus'. Could you point out what I am missing? Since I don't have platforms which have many cores and huge memory, I cannot play with this series on them. >>> The alternative is to defining CONFIG_ARCH_THREAD_INFO_ALLOCATOR and >>> allocate all stack memory from arch code. (Largely copied code, prevents >>> irq stacks being a different size, and nothing uses that define today!) >>> >>> >>> Thoughts? >> >> Almost same story I've been testing. >> >> I'm aligned with yours Regarding CONFIG_ARCH_THREAD_INFO_ALLOCATOR. >> >> Another approach I've tried is the following data structure, but it's not >> a good fit for this case due to __per_cpu_offset which is page-size aligned, >> not thread-size. >> >> struct irq_stack { >> char stack[THREAD_SIZE]; >> char *highest; >> } __aligned(THREAD_SIZE); >> >> DEFINE_PER_CPU(struct irq_stack, irq_stacks); > > Yes, x86 does this - but it increases the Image size by 16K, as that space > could have some initialisation values. This isn't a problem on x86 as > no-one uses the uncompressed image. > > I would avoid this approach due to the bloat! > >> >> ----8<----- >> diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h >> index 6ea82e8..d3619b3 100644 >> --- a/arch/arm64/include/asm/irq.h >> +++ b/arch/arm64/include/asm/irq.h >> @@ -1,7 +1,9 @@ >> #ifndef __ASM_IRQ_H >> #define __ASM_IRQ_H >> >> +#include <linux/gfp.h> >> #include <linux/irqchip/arm-gic-acpi.h> >> +#include <linux/slab.h> >> >> #include <asm-generic/irq.h> >> >> @@ -9,6 +11,21 @@ struct irq_stack { >> void *stack; >> }; >> >> +#if THREAD_SIZE >= PAGE_SIZE >> +static inline void *__alloc_irq_stack(void) >> +{ >> + return (void *)__get_free_pages(THREADINFO_GFP | __GFP_ZERO, >> + THREAD_SIZE_ORDER); >> +} >> +#else >> +extern struct kmem_cache *thread_info_cache; > > If this has been made a published symbol, it should go in a header file. Sure. >> + >> +static inline void *__alloc_irq_stack(void) >> +{ >> + return kmem_cache_alloc(thread_info_cache, THREADINFO_GFP | __GFP_ZERO); >> +} >> +#endif >> + >> struct pt_regs; >> >> extern void migrate_irqs(void); >> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c >> index a6bdf4d..4e13bdd 100644 >> --- a/arch/arm64/kernel/irq.c >> +++ b/arch/arm64/kernel/irq.c >> @@ -50,10 +50,13 @@ void __init set_handle_irq(void (*handle_irq)(struct pt_regs *)) >> handle_arch_irq = handle_irq; >> } >> >> +static char boot_irq_stack[THREAD_SIZE] __aligned(THREAD_SIZE); >> + >> void __init init_IRQ(void) >> { >> - if (alloc_irq_stack(smp_processor_id())) >> - panic("Failed to allocate IRQ stack for a boot cpu"); >> + unsigned int cpu = smp_processor_id(); >> + >> + per_cpu(irq_stacks, cpu).stack = boot_irq_stack + THREAD_START_SP; >> >> irqchip_init(); >> if (!handle_arch_irq) >> @@ -128,7 +131,7 @@ int alloc_irq_stack(unsigned int cpu) >> if (per_cpu(irq_stacks, cpu).stack) >> return 0; >> >> - stack = (void *)__get_free_pages(THREADINFO_GFP, THREAD_SIZE_ORDER); >> + stack = __alloc_irq_stack(); >> if (!stack) >> return -ENOMEM; >> >> diff --git a/kernel/fork.c b/kernel/fork.c >> index 2845623..9c55f86 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -172,7 +172,7 @@ static inline void free_thread_info(struct thread_info *ti) >> free_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER); >> } >> # else >> -static struct kmem_cache *thread_info_cache; >> +struct kmem_cache *thread_info_cache; >> >> static struct thread_info *alloc_thread_info_node(struct task_struct *tsk, >> int node) >> ----8<----- > > > Looks good! Thanks for reviewing the code! Best Regards Jungseok Lee-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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