dm crypt: add 'submit_from_crypt_cpus' option
Make it possible to disable offloading writes by setting the optional
'submit_from_crypt_cpus' table argument.
There are some situations where offloading write bios from the
encryption threads to a single thread degrades performance
significantly.
The default is to offload write bios to the same thread because it
benefits CFQ to have writes submitted using the same IO context.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/Documentation/device-mapper/dm-crypt.txt b/Documentation/device-mapper/dm-crypt.txt
index 571f24f..ad69778 100644
--- a/Documentation/device-mapper/dm-crypt.txt
+++ b/Documentation/device-mapper/dm-crypt.txt
@@ -51,7 +51,7 @@
Otherwise #opt_params is the number of following arguments.
Example of optional parameters section:
- 2 allow_discards same_cpu_crypt
+ 3 allow_discards same_cpu_crypt submit_from_crypt_cpus
allow_discards
Block discard requests (a.k.a. TRIM) are passed through the crypt device.
@@ -68,6 +68,14 @@
The default is to use an unbound workqueue so that encryption work
is automatically balanced between available CPUs.
+submit_from_crypt_cpus
+ Disable offloading writes to a separate thread after encryption.
+ There are some situations where offloading write bios from the
+ encryption threads to a single thread degrades performance
+ significantly. The default is to offload write bios to the same
+ thread because it benefits CFQ to have writes submitted using the
+ same context.
+
Example scripts
===============
LUKS (Linux Unified Key Setup) is now the preferred way to set up disk