PMEM read media monitored when issuing NTSTORE 256B writes

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Hao Guo

May 10, 2022, 3:53:43 AM5/10/22
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When I use "pmem_memcpy(p_start, arr, 256, PMEM_F_MEM_NONTEMPORAL)" in PMDK to issue NTSTORE 256B writes to PMEM, and use "ipmctl show -dimm -performance TotalMediaReads" to monitor media read counter at the same time, I discovered that the read counter is increasing at almost the same speed as the write counter, which can be monitored by command "ipmctl show -dimm -performance TotalMediaWrites". But the read request counter ("ipmctl show -dimm -performance TotalReadRequests") shows no increase. Why read media can be monitored at this pure-aligned-write workload? Thanks in advance!

Wu, Dennis

May 11, 2022, 3:00:01 AM5/11/22
to Hao Guo, pmem

PMem internal is a Read-Modify-Write, so you modify the media status, it will have the write. But if you monitor from the DDR-T bus like the pcm, you will not see any read BW.

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Hao Guo

May 12, 2022, 3:47:35 AM5/12/22
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Thanks for your consideration and timely reply! I have another question. Does **any** granuality of PMem write cause PMem read-modify-write inside PMem? If so, will PMem write operations influence read operations' bandwidth? That is, if I issue a read op at 6GB/s, then issue a write op at 2GB/s, will the read op's bandwidth drop to less than 4GB/s?
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