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4e893ca811
Use async function calls to make namespace scanning happen in parallel.
Without the patch, NVME namespaces are scanned serially, so it can take
a long time for all of a controller's namespaces to become available,
especially with a slower (TCP) interface with large number of
namespaces.
It is not uncommon to have large numbers (hundreds or thousands) of
namespaces on nvme-of with storage servers.
The time it took for all namespaces to show up after connecting (via
TCP) to a controller with 1002 namespaces was measured on one system:
network latency without patch with patch
0 6s 1s
50ms 210s 10s
100ms 417s 18s
Measurements taken on another system show the effect of the patch on the
time nvme_scan_work() took to complete, when connecting to a linux
nvme-of target with varying numbers of namespaces, on a network of
400us.
namespaces without patch with patch
1 16ms 14ms
2 24ms 16ms
4 49ms 22ms
8 101ms 33ms
16 207ms 56ms
100 1.4s 0.6s
1000 12.9s 2.0s
On the same system, connecting to a local PCIe NVMe drive (a Samsung
PM1733) instead of a network target:
namespaces without patch with patch
1 13ms 12ms
2 41ms 13ms
Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.