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Filename Latest commit message Latest commit date
Paolo Valente 3726112ec7 block, bfq: re-schedule empty queues if they deserve I/O plugging
Consider, on one side, a bfq_queue Q that remains empty while in
service, and, on the other side, the pending I/O of bfq_queues that,
according to their timestamps, have to be served after Q.  If an
uncontrolled amount of I/O from the latter bfq_queues were dispatched
while Q is waiting for its new I/O to arrive, then Q's bandwidth
guarantees would be violated. To prevent this, I/O dispatch is plugged
until Q receives new I/O (except for a properly controlled amount of
injected I/O). Unfortunately, preemption breaks I/O-dispatch plugging,
for the following reason.

Preemption is performed in two steps. First, Q is expired and
re-scheduled. Second, the new bfq_queue to serve is chosen. The first
step is needed by the second, as the second can be performed only
after Q's timestamps have been properly updated (done in the
expiration step), and Q has been re-queued for service. This
dependency is a consequence of the way how BFQ's scheduling algorithm
is currently implemented.

But Q is not re-scheduled at all in the first step, because Q is
empty. As a consequence, an uncontrolled amount of I/O may be
dispatched until Q becomes non empty again. This breaks Q's service
guarantees.

This commit addresses this issue by re-scheduling Q even if it is
empty. This in turn breaks the assumption that all scheduled queues
are non empty. Then a few extra checks are now needed.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-06-25 09:07:35 -06:00
arch arm64 fixes for -rc5 2019-06-14 06:16:47 -10:00
block block, bfq: re-schedule empty queues if they deserve I/O plugging 2019-06-25 09:07:35 -06:00
certs
crypto SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
Documentation Documentation: nvme: add an example for nvme fault injection 2019-06-21 11:15:50 +02:00
drivers Merge branch 'nvme-5.3' of git://git.infradead.org/nvme into for-5.3/block 2019-06-24 10:10:35 -06:00
fs blkcg, writeback: dead memcgs shouldn't contribute to writeback ownership arbitration 2019-06-15 10:39:42 -06:00
include nvme-trace: support for fabrics commands in host-side 2019-06-21 11:12:22 +02:00
init block: rename CONFIG_DEBUG_BLK_CGROUP to CONFIG_BFQ_CGROUP_DEBUG 2019-06-20 10:32:35 -06:00
ipc treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
kernel cgroup: export css_next_descendant_pre for bfq 2019-06-21 02:48:34 -06:00
lib lib/genalloc: introduce chunk owners 2019-06-13 17:34:56 -10:00
LICENSES
mm mm/devm_memremap_pages: fix final page put race 2019-06-13 17:34:56 -10:00
net SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
samples SPDX update for 5.2-rc4 2019-06-08 12:52:42 -07:00
scripts scripts/decode_stacktrace.sh: prefix addr2line with $CROSS_COMPILE 2019-06-13 17:34:56 -10:00
security Smack: Restore the smackfsdef mount option and add missing prefixes 2019-06-14 14:25:04 -10:00
sound sound fixes for 5.2-rc5 2019-06-14 05:37:06 -10:00
tools mm/devm_memremap_pages: fix final page put race 2019-06-13 17:34:56 -10:00
usr
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2019-06-08 12:48:49 -07:00
Makefile Linux 5.2-rc4 2019-06-08 20:24:46 -07:00
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.