[Bug 258295] nvme initialization may be unnecessarily slow

From: <bugzilla-noreply_at_freebsd.org>
Date: Sun, 05 Sep 2021 22:02:25 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=258295

            Bug ID: 258295
           Summary: nvme initialization may be unnecessarily slow
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: cperciva@FreeBSD.org

Initialization of nvme(4) devices includes two 100 ms pause(9) calls while
resetting the devices, along with a number of shorter delays; on EC2, about 335
ms is spent in nvme_ctrlr_start_config_hook.

Linux recently replaced a 100 ms wait with 1 ms waits plus polling the device
to see if it was ready; it would be nice if we could do something similar,
since the time spent in nvme initialization is now a nontrivial proportion of
kernel boot time.

https://www.phoronix.com/scan.php?page=news_item&px=NVMe-Faster-Linux-5.7-Boot

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