Software Tuning, Performance Optimization & Platform Monitoring
Discussion regarding monitoring and software tuning methodologies, Performance Monitoring Unit (PMU) of Intel microprocessors, and platform updating.

Questions on several L2 events in SNB



I'm tuning 462.libquantum with PMU events in SNB. Several L2 events confuse me.

1) l2_rqsts.pf_hit (24H:40H): Requests from L2 Hardware prefetcher that hit L2.
What's L2 Hardware prefetcher?  Where the data it prefetchs go? Why it access L2?
There are two types of prefetchres in SNB according to the Intel manual. One is "prefetch to L1" and another is "prefetch to L2/LLC". My understanding is that L2 Hardware prefetchre belongs to the latter. Right? 

2) What's the difference between l2_rqsts.all_demand_data_rd (24H:03H) and l2_trans.demand_data_rd (F0H:01H)?
l2_rqsts.all_demand_data_rd: Counts any demand and L1 HW prefetch data load request to L2.
l2_trans.demand_data_rd: Demand data read requests tha access L2 Cache
That is, l2_rqsts.all_demand_data_rd - l2_trans.demand_data_rd = Number of L1 HW prefetches?

3) What's LLC prefetch? I see the term in the description of l2_trans.all_pf. "L2 or LLC prefetches that access L2"

Thanks a ton!

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