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Subject[PATCH V2 0/3] block: set ioprio value
Date
Hi,

While experimenting with the ionice, I came across the scenario where
I cannot see the bio/request priority field being set when using
blkdiscard for REQ_OP_DISCARD, REQ_OP_WRITE_ZEROES and other operations
like REQ_OP_WRITE_SAME, REQ_OP_ZONE_RESET, and flush.

This is a small patch-series which sets the ioprio value at various
places for the zone-reset, flush, write-zeroes and discard operations.
This patch series uses get_current_ioprio() so that bio associated
with the respective operation can inherit the value from current
process.

In order to test this, I've modified the null_blk and enabled the
write_zeroes through module param. Following are the results.

Without these patches:-

# modprobe null_blk gb=5 nr_devices=1 write_zeroes=1
# for prio in `seq 0 3`; do ionice -c ${prio} blkdiscard -z -o 0 -l 4096 /dev/nullb0; done
# dmesg -c
[ 402.958458] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 0
[ 402.966024] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 0
[ 402.973960] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 0
[ 402.981373] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 0
#

With these patches:-

# modprobe null_blk gb=5 nr_devices=1 write_zeroes=1
# for prio in `seq 0 3`; do ionice -c ${prio} blkdiscard -z -o 0 -l 4096 /dev/nullb0; done
# dmesg -c
[ 1426.091772] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 0
[ 1426.100177] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 1
[ 1426.108035] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 2
[ 1426.115768] null_handle_cmd REQ_OP_WRITE_ZEROES priority class 3
#

With the block trace extension support is being worked on [1] which has
the ability to report the I/O priority, now we can track the correct
priority values with this patch-series.

Regards,
Chaitanya

[1] https://www.spinics.net/lists/linux-btrace/msg00880.html

* Changes from V1:-
1. Adjust the code for new changes from linux-block/for-next.

Chaitanya Kulkarni (3):
block: set ioprio for zone-reset bio
block: set ioprio for flush bio
block: set ioprio for discard, write-zeroes etc

block/blk-flush.c | 1 +
block/blk-lib.c | 4 ++++
block/blk-zoned.c | 2 ++
3 files changed, 7 insertions(+)

--
2.17.0

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