mainlining shenanigans
c663e04097
Currently, kcopyd has a sub-job size of 64KB and a maximum number of 8
sub-jobs. As a result, for any kcopyd job, we have a maximum of 512KB of
I/O in flight.
This upper limit to the amount of in-flight I/O under-utilizes fast
devices and results in decreased throughput, e.g., when writing to a
snapshotted thin LV with I/O size less than the pool's block size (so
COW is performed using kcopyd).
Increase kcopyd's default sub-job size to 512KB, so we have a maximum of
4MB of I/O in flight for each kcopyd job. This results in an up to 96%
improvement of bandwidth when writing to a snapshotted thin LV, with I/O
sizes less than the pool's block size.
Also, add dm_mod.kcopyd_subjob_size_kb module parameter to allow users
to fine tune the sub-job size of kcopyd. The default value of this
parameter is 512KB and the maximum allowed value is 1024KB.
We evaluate the performance impact of the change by running the
snap_breaking_throughput benchmark, from the device mapper test suite
[1].
The benchmark:
1. Creates a 1G thin LV
2. Provisions the thin LV
3. Takes a snapshot of the thin LV
4. Writes to the thin LV with:
dd if=/dev/zero of=/dev/vg/thin_lv oflag=direct bs=<I/O size>
Running this benchmark with various thin pool block sizes and dd I/O
sizes (all combinations triggering the use of kcopyd) we get the
following results:
+-----------------+-------------+------------------+-----------------+
| Pool block size | dd I/O size | BW before (MB/s) | BW after (MB/s) |
+-----------------+-------------+------------------+-----------------+
| 1 MB | 256 KB | 242 | 280 |
| 1 MB | 512 KB | 238 | 295 |
| | | | |
| 2 MB | 256 KB | 238 | 354 |
| 2 MB | 512 KB | 241 | 380 |
| 2 MB | 1 MB | 245 | 394 |
| | | | |
| 4 MB | 256 KB | 248 | 412 |
| 4 MB | 512 KB | 234 | 432 |
| 4 MB | 1 MB | 251 | 474 |
| 4 MB | 2 MB | 257 | 504 |
| | | | |
| 8 MB | 256 KB | 239 | 420 |
| 8 MB | 512 KB | 256 | 431 |
| 8 MB | 1 MB | 264 | 467 |
| 8 MB | 2 MB | 264 | 502 |
| 8 MB | 4 MB | 281 | 537 |
+-----------------+-------------+------------------+-----------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 Restructured Text 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.