Re: Question about LLC-load-misses event

[Chulmin Kim <cmkim@core.kaist.ac.kr>]

2012-10-15 오후 10:07, Chulmin Kim 쓴 글:
> Hi, all.
>
> I'm currently evaluating memory performance of my own machine (intel
> x5650 cpu).
> My machine can have NUMA configuration, but it is under control. (only
> local mem access allowed)
>
> As i run STREAM benchmark, i monitor LLC cache misses using "perf"
> simultaneously.
To be specific, I used STREAM Copy benchmark (which just copies memory
space by "a[i]=b[i]" repeatedly using for loop.)
> (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?

>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>