Re: [RESEND][PATCH] mm: vmstats: tlb flush counters

[Ingo Molnar]

* Dave Hansen <dave@xxxxxxxx> wrote:

> I was investigating some TLB flush scaling issues and realized
> that we do not have any good methods for figuring out how many
> TLB flushes we are doing.
> 
> It would be nice to be able to do these in generic code, but the
> arch-independent calls don't explicitly specify whether we
> actually need to do remote flushes or not.  In the end, we really
> need to know if we actually _did_ global vs. local invalidations,
> so that leaves us with few options other than to muck with the
> counters from arch-specific code.
> 
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> ---
> 
>  linux.git-davehans/arch/x86/mm/tlb.c             |   18 ++++++++++++++----
>  linux.git-davehans/include/linux/vm_event_item.h |    5 +++++
>  linux.git-davehans/mm/vmstat.c                   |    5 +++++
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff -puN arch/x86/mm/tlb.c~tlb-vmstats arch/x86/mm/tlb.c
> --- linux.git/arch/x86/mm/tlb.c~tlb-vmstats	2013-07-16 16:41:56.476280350 -0700
> +++ linux.git-davehans/arch/x86/mm/tlb.c	2013-07-16 16:41:56.483280658 -0700
> @@ -103,6 +103,7 @@ static void flush_tlb_func(void *info)
>  	if (f->flush_mm != this_cpu_read(cpu_tlbstate.active_mm))
>  		return;
>  
> +	count_vm_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
>  	if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
>  		if (f->flush_end == TLB_FLUSH_ALL)
>  			local_flush_tlb();
> @@ -130,6 +131,7 @@ void native_flush_tlb_others(const struc
>  	info.flush_start = start;
>  	info.flush_end = end;
>  
> +	count_vm_event(NR_TLB_REMOTE_FLUSH);
>  	if (is_uv_system()) {
>  		unsigned int cpu;
>  
> @@ -149,6 +151,7 @@ void flush_tlb_current_task(void)
>  
>  	preempt_disable();
>  
> +	count_vm_event(NR_TLB_LOCAL_FLUSH_ALL);
>  	local_flush_tlb();
>  	if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
>  		flush_tlb_others(mm_cpumask(mm), mm, 0UL, TLB_FLUSH_ALL);
> @@ -211,16 +214,19 @@ void flush_tlb_mm_range(struct mm_struct
>  	act_entries = mm->total_vm > tlb_entries ? tlb_entries : mm->total_vm;
>  
>  	/* tlb_flushall_shift is on balance point, details in commit log */
> -	if ((end - start) >> PAGE_SHIFT > act_entries >> tlb_flushall_shift)
> +	if ((end - start) >> PAGE_SHIFT > act_entries >> tlb_flushall_shift) {
> +		count_vm_event(NR_TLB_LOCAL_FLUSH_ALL);
>  		local_flush_tlb();
> -	else {
> +	} else {
>  		if (has_large_page(mm, start, end)) {
>  			local_flush_tlb();
>  			goto flush_all;
>  		}
>  		/* flush range by one by one 'invlpg' */
> -		for (addr = start; addr < end;	addr += PAGE_SIZE)
> +		for (addr = start; addr < end;	addr += PAGE_SIZE) {
> +			count_vm_event(NR_TLB_LOCAL_FLUSH_ONE);
>  			__flush_tlb_single(addr);
> +		}
>  
>  		if (cpumask_any_but(mm_cpumask(mm),
>  				smp_processor_id()) < nr_cpu_ids)
> @@ -256,6 +262,7 @@ void flush_tlb_page(struct vm_area_struc
>  
>  static void do_flush_tlb_all(void *info)
>  {
> +	count_vm_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
>  	__flush_tlb_all();
>  	if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_LAZY)
>  		leave_mm(smp_processor_id());
> @@ -263,6 +270,7 @@ static void do_flush_tlb_all(void *info)
>  
>  void flush_tlb_all(void)
>  {
> +	count_vm_event(NR_TLB_REMOTE_FLUSH);
>  	on_each_cpu(do_flush_tlb_all, NULL, 1);
>  }
>  
> @@ -272,8 +280,10 @@ static void do_kernel_range_flush(void *
>  	unsigned long addr;
>  
>  	/* flush range by one by one 'invlpg' */
> -	for (addr = f->flush_start; addr < f->flush_end; addr += PAGE_SIZE)
> +	for (addr = f->flush_start; addr < f->flush_end; addr += PAGE_SIZE) {
> +		count_vm_event(NR_TLB_LOCAL_FLUSH_ONE_KERNEL);
>  		__flush_tlb_single(addr);
> +	}
>  }
>  
>  void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> diff -puN include/linux/vm_event_item.h~tlb-vmstats include/linux/vm_event_item.h
> --- linux.git/include/linux/vm_event_item.h~tlb-vmstats	2013-07-16 16:41:56.478280438 -0700
> +++ linux.git-davehans/include/linux/vm_event_item.h	2013-07-16 16:41:56.483280658 -0700
> @@ -70,6 +70,11 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS
>  		THP_ZERO_PAGE_ALLOC,
>  		THP_ZERO_PAGE_ALLOC_FAILED,
>  #endif
>
> +		NR_TLB_REMOTE_FLUSH,	/* cpu tried to flush others' tlbs */
> +		NR_TLB_REMOTE_FLUSH_RECEIVED,/* cpu received ipi for flush */
> +		NR_TLB_LOCAL_FLUSH_ALL,
> +		NR_TLB_LOCAL_FLUSH_ONE,
> +		NR_TLB_LOCAL_FLUSH_ONE_KERNEL,

Please fix the vertical alignment of comments.

>  		NR_VM_EVENT_ITEMS
>  };
>  
> diff -puN mm/vmstat.c~tlb-vmstats mm/vmstat.c
> --- linux.git/mm/vmstat.c~tlb-vmstats	2013-07-16 16:41:56.480280525 -0700
> +++ linux.git-davehans/mm/vmstat.c	2013-07-16 16:41:56.484280703 -0700
> @@ -817,6 +817,11 @@ const char * const vmstat_text[] = {
>  	"thp_zero_page_alloc",
>  	"thp_zero_page_alloc_failed",
>  #endif
> +	"nr_tlb_remote_flush",
> +	"nr_tlb_remote_flush_received",
> +	"nr_tlb_local_flush_all",
> +	"nr_tlb_local_flush_one",
> +	"nr_tlb_local_flush_one_kernel",

At first sight this seems pretty x86 specific. No range flush events, etc.

But no strong objections from me, if Andrew likes it.

Thanks,

	Ingo
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