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dm crypt: add 'submit_from_crypt_cpus' option

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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>
This commit is contained in:
Mikulas Patocka 2015-02-13 08:27:08 -05:00 committed by Mike Snitzer
parent dc2676210c
commit 0f5d8e6ee7
2 changed files with 23 additions and 3 deletions
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10
Documentation/device-mapper/dm-crypt.txt
View file

@ -51,7 +51,7 @@ Parameters: <cipher> <key> <iv_offset> <device path> \
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 @@ same_cpu_crypt
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

16
drivers/md/dm-crypt.c
View file

@ -110,7 +110,8 @@ struct iv_tcw_private {
* Crypt: maps a linear range of a block device
* and encrypts / decrypts at the same time.
*/
enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID, DM_CRYPT_SAME_CPU };
enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID,
DM_CRYPT_SAME_CPU, DM_CRYPT_NO_OFFLOAD };
/*
* The fields in here must be read only after initialization.
@ -1239,6 +1240,11 @@ static void kcryptd_crypt_write_io_submit(struct dm_crypt_io *io, int async)
clone->bi_iter.bi_sector = cc->start + io->sector;
if (likely(!async) && test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags)) {
generic_make_request(clone);
return;
}
spin_lock_irqsave(&cc->write_thread_wait.lock, flags);
list_add_tail(&io->list, &cc->write_thread_list);
wake_up_locked(&cc->write_thread_wait);
@ -1693,7 +1699,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
char dummy;
static struct dm_arg _args[] = {
{0, 2, "Invalid number of feature args"},
{0, 3, "Invalid number of feature args"},
};
if (argc < 5) {
@ -1802,6 +1808,9 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
else if (!strcasecmp(opt_string, "same_cpu_crypt"))
set_bit(DM_CRYPT_SAME_CPU, &cc->flags);
else if (!strcasecmp(opt_string, "submit_from_crypt_cpus"))
set_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags);
else {
ti->error = "Invalid feature arguments";
goto bad;
@ -1905,12 +1914,15 @@ static void crypt_status(struct dm_target *ti, status_type_t type,
num_feature_args += !!ti->num_discard_bios;
num_feature_args += test_bit(DM_CRYPT_SAME_CPU, &cc->flags);
num_feature_args += test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags);
if (num_feature_args) {
DMEMIT(" %d", num_feature_args);
if (ti->num_discard_bios)
DMEMIT(" allow_discards");
if (test_bit(DM_CRYPT_SAME_CPU, &cc->flags))
DMEMIT(" same_cpu_crypt");
if (test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags))
DMEMIT(" submit_from_crypt_cpus");
}
break;