Re: Question about LLC-load-misses event

[Namhyung Kim <namhyung@kernel.org>]

Hi Chulmin,

On Mon, 15 Oct 2012 22:31:34 +0900, Chulmin Kim wrote:
> 2012-10-15 오후 10:07, Chulmin Kim 쓴 글:
>> (perf command : perf stat -a -A -e LLC-loads -e LLC-load-misses -e
>> instructions sleep 3)
>>
>> The problem is,, the bandwidth from STREAM benchmark does not match with
>> the monitored value.
>>
>> e.g.
>> I got 9395MB/s from Stream.
>>
>> "perf" shows 134,642,063 LLC-load-misses for 3 seconds.
>> -> BW = ((# of events)/(3 seconds)) * 64 bytes / (1024*1024) = 2739MB/s
>> In this equation, the term (64bytes) is for cache line size, and the
>> term(1024*1024) is for (MB/s).
>>
>> Why does this mismatch occur?
> In case of Oprofile, the value for a certain event represents the number
> of the overflows which occur when the number of the event exceeds the
> predefined value.
> Is it a similar case with that?

I guess not.  And what's the result of the LLC-loads?  AFAIK it counts
all cache accesses including hits and misses.  Did you calculate the
bandwidth using the result of LLC-loads?  I suspect the h/w *might*
prefetches a couple of lines when cache-miss occurred, but I'm not
sure. :)

Thanks,
Namhyung