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Commit 0f5d8e6e authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent dc267621

Documentation/device-mapper/dm-crypt.txt

+9 −1
Original line number Diff line number Diff line
@@ -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

drivers/md/dm-crypt.c

+14 −2
Original line number Diff line number Diff line
@@ -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;