The precision loss of reading IO start_time with jiffies_to_nsecs
instead of using a high resolution timer degrades HST path prediction
for BIO-based mpath on high load workloads.
Below, I show the utilization percentage of a 10 disk multipath with
asymmetrical disk access cost, while being exercised by a randwrite FIO
benchmark with high submission queue depth (depth=64). It is possible
to see that the HST path selection degrades heavily for high-iops in
BIO-mpath, underutilizing the slower paths way beyond expected. This
seems to be caused by the start_time truncation, which makes some IO to
seem much slower than it actually is. In this scenario ST outperforms
HST for bio-mpath, but not for mq-mpath, which already uses ktime_get_ns().
The third column shows utilization with this patch applied. It is easy
to see that now HST prediction is much closer to the ideal distribution
(calculated considering the real cost of each path).
| | ST | HST (orig) | HST(ktime) | Best |
| sdd | 0.17 | 0.20 | 0.17 | 0.18 |
| sde | 0.17 | 0.20 | 0.17 | 0.18 |
| sdf | 0.17 | 0.20 | 0.17 | 0.18 |
| sdg | 0.06 | 0.00 | 0.06 | 0.04 |
| sdh | 0.03 | 0.00 | 0.03 | 0.02 |
| sdi | 0.03 | 0.00 | 0.03 | 0.02 |
| sdj | 0.02 | 0.00 | 0.01 | 0.01 |
| sdk | 0.02 | 0.00 | 0.01 | 0.01 |
| sdl | 0.17 | 0.20 | 0.17 | 0.18 |
| sdm | 0.17 | 0.20 | 0.17 | 0.18 |
This issue was originally discussed [1] when we first merged HST, and
this patch was left as a low hanging fruit to be solved later.
Regarding the implementation, as suggested by Mike in that mail thread,
in order to avoid the overhead of ktime_get_ns for other selectors, this
patch adds a flag for the selector code to request the high-resolution
timer.
I tested this using the same benchmark used in the original HST submission.
Full test and benchmark scripts are available here:
https://people.collabora.com/~krisman/HST-BIO-MPATH/
[1] https://lore.kernel.org/lkml/85tv0am9de.fsf@collabora.com/T/
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
[snitzer: cleaned up various implementation details]
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Mixing sched_clock() and ktime_get_ns() usage will give bad results.
Switch hst_select_path() from using sched_clock() to ktime_get_ns().
Also rename path_service_time()'s 'sched_now' variable to 'now'.
Fixes: 2613eab119 ("dm mpath: add Historical Service Time Path Selector")
Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Drop various include not actually used in blkdev.h itself.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210920123328.1399408-14-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
For device mapper targets to take advantage of IMA's measurement
capabilities, the status functions for the individual targets need to be
updated to handle the status_type_t case for value STATUSTYPE_IMA.
Update status functions for the following target types, to log their
respective attributes to be measured using IMA.
01. cache
02. crypt
03. integrity
04. linear
05. mirror
06. multipath
07. raid
08. snapshot
09. striped
10. verity
For rest of the targets, handle the STATUSTYPE_IMA case by setting the
measurement buffer to NULL.
For IMA to measure the data on a given system, the IMA policy on the
system needs to be updated to have the following line, and the system
needs to be restarted for the measurements to take effect.
/etc/ima/ima-policy
measure func=CRITICAL_DATA label=device-mapper template=ima-buf
The measurements will be reflected in the IMA logs, which are located at:
/sys/kernel/security/integrity/ima/ascii_runtime_measurements
/sys/kernel/security/integrity/ima/binary_runtime_measurements
These IMA logs can later be consumed by various attestation clients
running on the system, and send them to external services for attesting
the system.
The DM target data measured by IMA subsystem can alternatively
be queried from userspace by setting DM_IMA_MEASUREMENT_FLAG with
DM_TABLE_STATUS_CMD.
Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Additional prefix helps clarify that these source files implement path
selectors.
Required updating Makefile to still build modules _without_ the
"dm-ps" prefix to preserve dm-multipath's ability to autoload path
selector modules. While at it, cleaned up some DM whitespace in
Makefile.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
