On 04/24/2014 03:14 AM, Mel Gorman wrote:
> On Mon, Apr 21, 2014 at 11:24:25AM -0700, Dave Hansen wrote:
>> @@ -105,9 +108,10 @@ static void flush_tlb_func(void *info)
>>
>> count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
>> if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
>> - if (f->flush_end == TLB_FLUSH_ALL)
>> + if (f->flush_end == TLB_FLUSH_ALL) {
>> local_flush_tlb();
>> - else if (!f->flush_end)
>> + trace_tlb_flush(TLB_REMOTE_SHOOTDOWN, TLB_FLUSH_ALL);
>> + } else if (!f->flush_end)
>> __flush_tlb_single(f->flush_start);
>> else {
>> unsigned long addr;
>
> Why is only the TLB_FLUSH_ALL case traced here and not the single flush
> or range of flushes? __native_flush_tlb_single() doesn't have a trace
> point so I worry we are missing visibility on this part in particular
> this part.
>
> while (addr < f->flush_end) {
> __flush_tlb_single(addr);
> addr += PAGE_SIZE;
> }
You're right, I missed that bit. I've corrected in a later version of
the patch.
>> @@ -152,7 +156,9 @@ void flush_tlb_current_task(void)
>> preempt_disable();
>>
>> count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
>> + trace_tlb_flush(TLB_LOCAL_SHOOTDOWN, TLB_FLUSH_ALL);
>> local_flush_tlb();
>> + trace_tlb_flush(TLB_LOCAL_SHOOTDOWN_DONE, TLB_FLUSH_ALL);
>> if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
>> flush_tlb_others(mm_cpumask(mm), mm, 0UL, TLB_FLUSH_ALL);
>> preempt_enable();
>
> Are the two tracepoints really useful? Are they fine enough to measure
> the cost of the TLB flush? It misses the refill obviously but not much
> we can do there.
It's fine enough, but I did realize over time that the cost of the
tracepoint is about 3x the cost of a 1-page tlb flush itself, so these
are unusable for detailed measurements. I'll remove it for now.
>> #endif /* _LINUX_MM_TYPES_H */
>> diff -puN /dev/null include/trace/events/tlb.h
>> --- /dev/null 2014-04-10 11:28:14.066815724 -0700
>> +++ b/include/trace/events/tlb.h 2014-04-21 11:10:35.529868198 -0700
>> @@ -0,0 +1,37 @@
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM tlb
>> +
>> +#if !defined(_TRACE_TLB_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_TLB_H
>> +
>> +#include <linux/mm_types.h>
>> +#include <linux/tracepoint.h>
>> +
>> +extern const char * const tlb_flush_reason_desc[];
>> +
>> +TRACE_EVENT(tlb_flush,
>> +
>> + TP_PROTO(int reason, unsigned long pages),
>> + TP_ARGS(reason, pages),
>> +
>> + TP_STRUCT__entry(
>> + __field( int, reason)
>> + __field(unsigned long, pages)
>> + ),
>> +
>> + TP_fast_assign(
>> + __entry->reason = reason;
>> + __entry->pages = pages;
>> + ),
>> +
>> + TP_printk("pages: %ld reason: %d (%s)",
>> + __entry->pages,
>> + __entry->reason,
>> + tlb_flush_reason_desc[__entry->reason])
>> +);
>> +
>
> I would also suggest you match the output formatting with writeback.h
> which would look like
>
> pages:%lu reason:%s
>
> The raw format should still have the integer while the string formatting
> would have something human readable.
I can do that. The only bummer with the human-readable strings is
turning them back in to something that the filters can take. I think
I'll just do:
+ TP_printk("pages:%ld reason:%s (%d)",
+ __entry->pages,
+ __print_symbolic(__entry->reason, TLB_FLUSH_REASON),
+ __entry->reason)
+);
--
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