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Jan Kara f34142ab4e md/raid0: Fix performance regression for large sequential writes 
[ Upstream commit 319ff40a54 ]

Commit f00d7c85be ("md/raid0: fix up bio splitting.") among other
things changed how bio that needs to be split is submitted. Before this
commit, we have split the bio, mapped and submitted each part. After
this commit, we map only the first part of the split bio and submit the
second part unmapped. Due to bio sorting in __submit_bio_noacct() this
results in the following request ordering:

  9,0   18     1181     0.525037895 15995  Q  WS 1479315464 + 63392

  Split off chunk-sized (1024 sectors) request:

  9,0   18     1182     0.629019647 15995  X  WS 1479315464 / 1479316488

  Request is unaligned to the chunk so it's split in
  raid0_make_request().  This is the first part mapped and punted to
  bio_list:

  8,0   18     7053     0.629020455 15995  A  WS 739921928 + 1016 <- (9,0) 1479315464

  Now raid0_make_request() returns, second part is postponed on
  bio_list. __submit_bio_noacct() resorts the bio_list, mapped request
  is submitted to the underlying device:

  8,0   18     7054     0.629022782 15995  G  WS 739921928 + 1016

  Now we take another request from the bio_list which is the remainder
  of the original huge request. Split off another chunk-sized bit from
  it and the situation repeats:

  9,0   18     1183     0.629024499 15995  X  WS 1479316488 / 1479317512
  8,16  18     6998     0.629025110 15995  A  WS 739921928 + 1016 <- (9,0) 1479316488
  8,16  18     6999     0.629026728 15995  G  WS 739921928 + 1016
  ...
  9,0   18     1184     0.629032940 15995  X  WS 1479317512 / 1479318536 [libnetacq-write]
  8,0   18     7059     0.629033294 15995  A  WS 739922952 + 1016 <- (9,0) 1479317512
  8,0   18     7060     0.629033902 15995  G  WS 739922952 + 1016
  ...

  This repeats until we consume the whole original huge request. Now we
  finally get to processing the second parts of the split off requests
  (in reverse order):

  8,16  18     7181     0.629161384 15995  A  WS 739952640 + 8 <- (9,0) 1479377920
  8,0   18     7239     0.629162140 15995  A  WS 739952640 + 8 <- (9,0) 1479376896
  8,16  18     7186     0.629163881 15995  A  WS 739951616 + 8 <- (9,0) 1479375872
  8,0   18     7242     0.629164421 15995  A  WS 739951616 + 8 <- (9,0) 1479374848
  ...

I guess it is obvious that this IO pattern is extremely inefficient way
to perform sequential IO. It also makes bio_list to grow to rather long
lengths.

Change raid0_make_request() to map both parts of the split bio. Since we
know we are provided with at most chunk-sized bios, we will always need
to split the incoming bio at most once.

Fixes: f00d7c85be ("md/raid0: fix up bio splitting.")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20230814092720.3931-2-jack@suse.cz
Signed-off-by: Song Liu <song@kernel.org>
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: Fix performance regression for large sequential writes 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.