On Mon, 6 Mar 2023, Mikulas Patocka wrote:
> > Hi,
> >
> > Thanks a lot for your review!
> >
> > It's ok to fix the softlockup, but for async write encrypt,
> > kcryptd_crypt_write_io_submit will add bio to write_tree, and once we
> > call cond_resched before every kcryptd_io_write, the write performance
> > may be poor while we meet a high cpu usage scene.
>
> Hi
>
> To fix this problem, find the PID of the process "dmcrypt_write" and
> change its priority to -20, for example "renice -n -20 -p 34748".
>
> This is the proper way how to fix it; locking up the process for one
> second is not.
>
> We used to have high-priority workqueues by default, but it caused audio
> playback skipping, so we had to revert it - see
> f612b2132db529feac4f965f28a1b9258ea7c22b.
>
> Perhaps we should add an option to have high-priority kernel threads?
>
> Mikulas
Here I'm sending a patch that makes it optional to raise the priority
of dm-crypt workqueues and the write thread. Test it, if it helps for you.
Mikulas
From: Mikulas Patocka <mpato...@redhat.com>
It was reported that dm-crypt performs badly when the system is loaded[1].
So I'm adding an option "high_priority" that sets the workqueues and the
write_thread to nice level -20. This used to be the default in the past,
but it caused audio skipping, so it had to be reverted - see the commit
f612b2132db529feac4f965f28a1b9258ea7c22b. This commit makes it optional,
so that normal users won't be harmed by it.
[1] https://listman.redhat.com/archives/dm-devel/2023-February/053410.html
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
---
Documentation/admin-guide/device-mapper/dm-crypt.rst | 5 +++
drivers/md/dm-crypt.c | 28 +++++++++++++------
2 files changed, 25 insertions(+), 8 deletions(-)
Index: linux-2.6/drivers/md/dm-crypt.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-crypt.c
+++ linux-2.6/drivers/md/dm-crypt.c
@@ -133,9 +133,9 @@ struct iv_elephant_private {
* and encrypts / decrypts at the same time.
*/
enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID,
- DM_CRYPT_SAME_CPU, DM_CRYPT_NO_OFFLOAD,
- DM_CRYPT_NO_READ_WORKQUEUE, DM_CRYPT_NO_WRITE_WORKQUEUE,
- DM_CRYPT_WRITE_INLINE };
+ DM_CRYPT_SAME_CPU, DM_CRYPT_HIGH_PRIORITY,
+ DM_CRYPT_NO_OFFLOAD, DM_CRYPT_NO_READ_WORKQUEUE,
+ DM_CRYPT_NO_WRITE_WORKQUEUE, DM_CRYPT_WRITE_INLINE };
enum cipher_flags {
CRYPT_MODE_INTEGRITY_AEAD, /* Use authenticated mode for cipher */
@@ -3087,7 +3087,7 @@ static int crypt_ctr_optional(struct dm_
struct crypt_config *cc = ti->private;
struct dm_arg_set as;
static const struct dm_arg _args[] = {
- {0, 8, "Invalid number of feature args"},
+ {0, 9, "Invalid number of feature args"},
};
unsigned int opt_params, val;
const char *opt_string, *sval;
@@ -3114,6 +3114,8 @@ static int crypt_ctr_optional(struct dm_
else if (!strcasecmp(opt_string, "same_cpu_crypt"))
set_bit(DM_CRYPT_SAME_CPU, &cc->flags);
+ else if (!strcasecmp(opt_string, "high_priority"))
+ set_bit(DM_CRYPT_HIGH_PRIORITY, &cc->flags);
else if (!strcasecmp(opt_string, "submit_from_crypt_cpus"))
set_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags);
@@ -3352,18 +3354,22 @@ static int crypt_ctr(struct dm_target *t
}
ret = -ENOMEM;
- cc->io_queue = alloc_workqueue("kcryptd_io/%s", WQ_MEM_RECLAIM, 1,
devname);
+ cc->io_queue = alloc_workqueue("kcryptd_io/%s", WQ_MEM_RECLAIM |
+ test_bit(DM_CRYPT_HIGH_PRIORITY,
&cc->flags) * WQ_HIGHPRI,
+ 1, devname);
if (!cc->io_queue) {
ti->error = "Couldn't create kcryptd io queue";
goto bad;
}
if (test_bit(DM_CRYPT_SAME_CPU, &cc->flags))
- cc->crypt_queue = alloc_workqueue("kcryptd/%s",
WQ_CPU_INTENSIVE | WQ_MEM_RECLAIM,
+ cc->crypt_queue = alloc_workqueue("kcryptd/%s",
WQ_CPU_INTENSIVE | WQ_MEM_RECLAIM |
+
test_bit(DM_CRYPT_HIGH_PRIORITY, &cc->flags) * WQ_HIGHPRI,
1, devname);
else
cc->crypt_queue = alloc_workqueue("kcryptd/%s",
- WQ_CPU_INTENSIVE |
WQ_MEM_RECLAIM | WQ_UNBOUND,
+ WQ_CPU_INTENSIVE |
WQ_MEM_RECLAIM | WQ_UNBOUND |
+
test_bit(DM_CRYPT_HIGH_PRIORITY, &cc->flags) * WQ_HIGHPRI,
num_online_cpus(), devname);
if (!cc->crypt_queue) {
ti->error = "Couldn't create kcryptd queue";
@@ -3380,6 +3386,8 @@ static int crypt_ctr(struct dm_target *t
ti->error = "Couldn't spawn write thread";
goto bad;
}
+ if (test_bit(DM_CRYPT_HIGH_PRIORITY, &cc->flags))
+ set_user_nice(cc->write_thread, MIN_NICE);
ti->num_flush_bios = 1;
ti->limit_swap_bios = true;
@@ -3500,6 +3508,7 @@ static void crypt_status(struct dm_targe
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_HIGH_PRIORITY,
&cc->flags);
num_feature_args += test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags);
num_feature_args += test_bit(DM_CRYPT_NO_READ_WORKQUEUE,
&cc->flags);
num_feature_args += test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE,
&cc->flags);
@@ -3513,6 +3522,8 @@ static void crypt_status(struct dm_targe
DMEMIT(" allow_discards");
if (test_bit(DM_CRYPT_SAME_CPU, &cc->flags))
DMEMIT(" same_cpu_crypt");
+ if (test_bit(DM_CRYPT_HIGH_PRIORITY, &cc->flags))
+ DMEMIT(" high_priority");
if (test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags))
DMEMIT(" submit_from_crypt_cpus");
if (test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags))
@@ -3532,6 +3543,7 @@ static void crypt_status(struct dm_targe
DMEMIT_TARGET_NAME_VERSION(ti->type);
DMEMIT(",allow_discards=%c", ti->num_discard_bios ? 'y' : 'n');
DMEMIT(",same_cpu_crypt=%c", test_bit(DM_CRYPT_SAME_CPU,
&cc->flags) ? 'y' : 'n');
+ DMEMIT(",high_priority=%c", test_bit(DM_CRYPT_HIGH_PRIORITY,
&cc->flags) ? 'y' : 'n');
DMEMIT(",submit_from_crypt_cpus=%c",
test_bit(DM_CRYPT_NO_OFFLOAD, &cc->flags) ?
'y' : 'n');
DMEMIT(",no_read_workqueue=%c",
test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags) ?
@@ -3659,7 +3671,7 @@ static void crypt_io_hints(struct dm_tar
static struct target_type crypt_target = {
.name = "crypt",
- .version = {1, 24, 0},
+ .version = {1, 25, 0},
.module = THIS_MODULE,
.ctr = crypt_ctr,
.dtr = crypt_dtr,
Index: linux-2.6/Documentation/admin-guide/device-mapper/dm-crypt.rst
===================================================================
--- linux-2.6.orig/Documentation/admin-guide/device-mapper/dm-crypt.rst
+++ linux-2.6/Documentation/admin-guide/device-mapper/dm-crypt.rst
@@ -113,6 +113,11 @@ same_cpu_crypt
The default is to use an unbound workqueue so that encryption work
is automatically balanced between available CPUs.
+high_priority
+ Set dm-crypt workqueues and the writer thread to high priority. This
+ improves throughput and latency of dm-crypt while degrading general
+ responsiveness of the system.
+
submit_from_crypt_cpus
Disable offloading writes to a separate thread after encryption.
There are some situations where offloading write bios from the
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