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David Jeffery 293c2dd9ed md: raid0: account for split bio in iostat accounting 
[ Upstream commit cc22b5407e ]

When a bio is split by md raid0, the newly created bio will not be tracked
by md for I/O accounting. Only the portion of I/O still assigned to the
original bio which was reduced by the split will be accounted for. This
results in md iostat data sometimes showing I/O values far below the actual
amount of data being sent through md.

md_account_bio() needs to be called for all bio generated by the bio split.

A simple example of the issue was generated using a raid0 device on partitions
to the same device. Since all raid0 I/O then goes to one device, it makes it
easy to see a gap between the md device and its sd storage. Reading an lvm
device on top of the md device, the iostat output (some 0 columns and extra
devices removed to make the data more compact) was:

Device             tps    kB_read/s    kB_wrtn/s    kB_dscd/s    kB_read
md2               0.00         0.00         0.00         0.00          0
sde               0.00         0.00         0.00         0.00          0
md2            1364.00    411496.00         0.00         0.00     411496
sde            1734.00    646144.00         0.00         0.00     646144
md2            1699.00    510680.00         0.00         0.00     510680
sde            2155.00    802784.00         0.00         0.00     802784
md2             803.00    241480.00         0.00         0.00     241480
sde            1016.00    377888.00         0.00         0.00     377888
md2               0.00         0.00         0.00         0.00          0
sde               0.00         0.00         0.00         0.00          0

I/O was generated doing large direct I/O reads (12M) with dd to a linear
lvm volume on top of the 4 leg raid0 device.

The md2 reads were showing as roughly 2/3 of the reads to the sde device
containing all of md2's raid partitions. The sum of reads to sde was
1826816 kB, which was the expected amount as it was the amount read by
dd. With the patch, the total reads from md will match the reads from
sde and be consistent with the amount of I/O generated.

Fixes: 10764815ff ("md: add io accounting for raid0 and raid5")
Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230816181433.13289-1-djeffery@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-09-13 09:48:19 +02:00
arch arm64: dts: qcom: sc8280xp-x13s: Unreserve NC pins 2023-09-13 09:48:18 +02:00
block blk-cgroup: Fix NULL deref caused by blkg_policy_data being installed before init 2023-09-13 09:48:19 +02:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto crypto: api - Use work queue in crypto_destroy_instance 2023-09-13 09:48:03 +02:00
Documentation dt-bindings: sc16is7xx: Add property to change GPIO function 2023-09-06 21:25:32 +01:00
drivers md: raid0: account for split bio in iostat accounting 2023-09-13 09:48:19 +02:00
fs quota: fix dqput() to follow the guarantees dquot_srcu should provide 2023-09-13 09:48:09 +02:00
include block: don't allow enabling a cache on devices that don't support it 2023-09-13 09:48:13 +02:00
init sched/psi: Select KERNFS as needed 2023-09-13 09:47:58 +02:00
io_uring io_uring: fix drain stalls by invalid SQE 2023-09-13 09:48:17 +02:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel audit: fix possible soft lockup in __audit_inode_child() 2023-09-13 09:48:17 +02:00
lib sbitmap: fix batching wakeup 2023-09-13 09:47:55 +02:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm net-memcg: Fix scope of sockmem pressure indicators 2023-09-13 09:48:05 +02:00
net netrom: Deny concurrent connect(). 2023-09-13 09:48:09 +02:00
rust rust: macros: vtable: fix HAS_* redefinition (gen_const_name) 2023-08-23 17:32:36 +02:00
samples samples/bpf: fix broken map lookup probe 2023-09-13 09:48:06 +02:00
scripts scripts/gdb: fix 'lx-lsmod' show the wrong size 2023-09-13 09:48:05 +02:00
security smackfs: Prevent underflow in smk_set_cipso() 2023-09-13 09:48:16 +02:00
sound ASoC: SOF: Intel: fix u16/32 confusion in LSDIID 2023-09-13 09:48:16 +02:00
tools selftests: memfd: error out test process when child test fails 2023-09-13 09:48:06 +02:00
usr initramfs: Check negative timestamp to prevent broken cpio archive 2023-04-16 17:37:01 +09:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-03 10:26:01 +02:00
.clang-format cxl for v6.4 2023-04-30 11:51:51 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore linux-kselftest-kunit-6.4-rc1 2023-04-24 12:31:32 -07:00
.mailmap mailmap: add entries for Ben Dooks 2023-06-19 13:19:35 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: sctp: move Neil to CREDITS 2023-05-12 08:51:32 +01:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 6.4-rc8, including fixes from ipsec, bpf, 2023-06-22 17:59:51 -07:00
Makefile kbuild: rust_is_available: remove -v option 2023-09-13 09:48:03 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.