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DAOS-19292 doc: warn against using PMEM_NO_FLUSH (#18703) #18948

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daltonbohning merged 1 commit into from
Sep 1, 2026
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DAOS-19292 doc: warn against using PMEM_NO_FLUSH (#18703) #18948

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20 changes: 16 additions & 4 deletions docs/admin/performance_tuning.md
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Expand Up @@ -398,10 +398,22 @@ Duration across processes:
Completed test=FETCH
```

!!! note
With 3rd Gen Intel® Xeon® Scalable processors (ICX), the PMEM_NO_FLUSH
environment variable can be set to 1 to take advantage of the extended
asynchronous DRAM refresh (eADR) feature
!!! warning
Do not set the `PMEM_NO_FLUSH` environment variable in production. This
document previously recommended setting `PMEM_NO_FLUSH=1` on 3rd Gen
Intel® Xeon® Scalable processors (ICX) to take advantage of the extended
asynchronous DRAM refresh (eADR) feature; **that guidance is deprecated
and must no longer be followed**.

Per PMDK's [libpmem(7)](https://github.com/daos-stack/pmdk/blob/stable-2.1/doc/libpmem/libpmem.7.md)
documentation, environment variables such as `PMEM_NO_FLUSH` are "largely
intended for testing and are not normally required". Setting
`PMEM_NO_FLUSH=1` unconditionally disables the
`CLFLUSH`/`CLFLUSHOPT`/`CLWB` cache-flush instructions, regardless of
whether the platform's persistence domain actually covers CPU caches.
PMDK already checks this safely and automatically at runtime via
[`pmem_has_auto_flush()`](https://github.com/daos-stack/pmdk/blob/stable-2.1/doc/libpmem/pmem_flush.3.md),
so no manual override should be used in production.

A tool called daos\_perf with the same syntax as vos\_perf is also available
to run tests from a compute node with the full DAOS stack. Please refer
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