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 (file)
--- a/Documentation/device-mapper/dm-crypt.txt
+++ b/Documentation/device-mapper/dm-crypt.txt
@@ -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

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 8c0e36b..4519a7c 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -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;