linux/Documentation/block/00-INDEX

35 lines
983 B
Plaintext
Raw Normal View History

00-INDEX
- This file
block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler We tag as v0 the version of BFQ containing only BFQ's engine plus hierarchical support. BFQ's engine is introduced by this commit, while hierarchical support is added by next commit. We use the v0 tag to distinguish this minimal version of BFQ from the versions containing also the features and the improvements added by next commits. BFQ-v0 coincides with the version of BFQ submitted a few years ago [1], apart from the introduction of preemption, described below. BFQ is a proportional-share I/O scheduler, whose general structure, plus a lot of code, are borrowed from CFQ. - Each process doing I/O on a device is associated with a weight and a (bfq_)queue. - BFQ grants exclusive access to the device, for a while, to one queue (process) at a time, and implements this service model by associating every queue with a budget, measured in number of sectors. - After a queue is granted access to the device, the budget of the queue is decremented, on each request dispatch, by the size of the request. - The in-service queue is expired, i.e., its service is suspended, only if one of the following events occurs: 1) the queue finishes its budget, 2) the queue empties, 3) a "budget timeout" fires. - The budget timeout prevents processes doing random I/O from holding the device for too long and dramatically reducing throughput. - Actually, as in CFQ, a queue associated with a process issuing sync requests may not be expired immediately when it empties. In contrast, BFQ may idle the device for a short time interval, giving the process the chance to go on being served if it issues a new request in time. Device idling typically boosts the throughput on rotational devices, if processes do synchronous and sequential I/O. In addition, under BFQ, device idling is also instrumental in guaranteeing the desired throughput fraction to processes issuing sync requests (see [2] for details). - With respect to idling for service guarantees, if several processes are competing for the device at the same time, but all processes (and groups, after the following commit) have the same weight, then BFQ guarantees the expected throughput distribution without ever idling the device. Throughput is thus as high as possible in this common scenario. - Queues are scheduled according to a variant of WF2Q+, named B-WF2Q+, and implemented using an augmented rb-tree to preserve an O(log N) overall complexity. See [2] for more details. B-WF2Q+ is also ready for hierarchical scheduling. However, for a cleaner logical breakdown, the code that enables and completes hierarchical support is provided in the next commit, which focuses exactly on this feature. - B-WF2Q+ guarantees a tight deviation with respect to an ideal, perfectly fair, and smooth service. In particular, B-WF2Q+ guarantees that each queue receives a fraction of the device throughput proportional to its weight, even if the throughput fluctuates, and regardless of: the device parameters, the current workload and the budgets assigned to the queue. - The last, budget-independence, property (although probably counterintuitive in the first place) is definitely beneficial, for the following reasons: - First, with any proportional-share scheduler, the maximum deviation with respect to an ideal service is proportional to the maximum budget (slice) assigned to queues. As a consequence, BFQ can keep this deviation tight not only because of the accurate service of B-WF2Q+, but also because BFQ *does not* need to assign a larger budget to a queue to let the queue receive a higher fraction of the device throughput. - Second, BFQ is free to choose, for every process (queue), the budget that best fits the needs of the process, or best leverages the I/O pattern of the process. In particular, BFQ updates queue budgets with a simple feedback-loop algorithm that allows a high throughput to be achieved, while still providing tight latency guarantees to time-sensitive applications. When the in-service queue expires, this algorithm computes the next budget of the queue so as to: - Let large budgets be eventually assigned to the queues associated with I/O-bound applications performing sequential I/O: in fact, the longer these applications are served once got access to the device, the higher the throughput is. - Let small budgets be eventually assigned to the queues associated with time-sensitive applications (which typically perform sporadic and short I/O), because, the smaller the budget assigned to a queue waiting for service is, the sooner B-WF2Q+ will serve that queue (Subsec 3.3 in [2]). - Weights can be assigned to processes only indirectly, through I/O priorities, and according to the relation: weight = 10 * (IOPRIO_BE_NR - ioprio). The next patch provides, instead, a cgroups interface through which weights can be assigned explicitly. - If several processes are competing for the device at the same time, but all processes and groups have the same weight, then BFQ guarantees the expected throughput distribution without ever idling the device. It uses preemption instead. Throughput is then much higher in this common scenario. - ioprio classes are served in strict priority order, i.e., lower-priority queues are not served as long as there are higher-priority queues. Among queues in the same class, the bandwidth is distributed in proportion to the weight of each queue. A very thin extra bandwidth is however guaranteed to the Idle class, to prevent it from starving. - If the strict_guarantees parameter is set (default: unset), then BFQ - always performs idling when the in-service queue becomes empty; - forces the device to serve one I/O request at a time, by dispatching a new request only if there is no outstanding request. In the presence of differentiated weights or I/O-request sizes, both the above conditions are needed to guarantee that every queue receives its allotted share of the bandwidth (see Documentation/block/bfq-iosched.txt for more details). Setting strict_guarantees may evidently affect throughput. [1] https://lkml.org/lkml/2008/4/1/234 https://lkml.org/lkml/2008/11/11/148 [2] P. Valente and M. Andreolini, "Improving Application Responsiveness with the BFQ Disk I/O Scheduler", Proceedings of the 5th Annual International Systems and Storage Conference (SYSTOR '12), June 2012. Slightly extended version: http://algogroup.unimore.it/people/paolo/disk_sched/bfq-v1-suite- results.pdf Signed-off-by: Fabio Checconi <fchecconi@gmail.com> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-19 14:29:02 +00:00
bfq-iosched.txt
- BFQ IO scheduler and its tunables
biodoc.txt
- Notes on the Generic Block Layer Rewrite in Linux 2.5
biovecs.txt
- Immutable biovecs and biovec iterators
capability.txt
- Generic Block Device Capability (/sys/block/<device>/capability)
cfq-iosched.txt
- CFQ IO scheduler tunables
cmdline-partition.txt
- how to specify block device partitions on kernel command line
data-integrity.txt
- Block data integrity
deadline-iosched.txt
- Deadline IO scheduler tunables
ioprio.txt
- Block io priorities (in CFQ scheduler)
pr.txt
- Block layer support for Persistent Reservations
Documentation/: update 00-INDEX files Some of the 00-INDEX files are somewhat outdated and some folders does not contain 00-INDEX at all. Only outdated (with the notably exception of spi) indexes are touched here, the 169 folders without 00-INDEX has not been touched. New 00-INDEX - spi/* was added in a series of commits dating back to 2006 Added files (missing in (*/)00-INDEX) - dmatest.txt was added by commit 851b7e16a07d ("dmatest: run test via debugfs") - this_cpu_ops.txt was added by commit a1b2a555d637 ("percpu: add documentation on this_cpu operations") - ww-mutex-design.txt was added by commit 040a0a371005 ("mutex: Add support for wound/wait style locks") - bcache.txt was added by commit cafe56359144 ("bcache: A block layer cache") - kernel-per-CPU-kthreads.txt was added by commit 49717cb40410 ("kthread: Document ways of reducing OS jitter due to per-CPU kthreads") - phy.txt was added by commit ff764963479a ("drivers: phy: add generic PHY framework") - block/null_blk was added by commit 12f8f4fc0314 ("null_blk: documentation") - module-signing.txt was added by commit 3cafea307642 ("Add Documentation/module-signing.txt file") - assoc_array.txt was added by commit 3cb989501c26 ("Add a generic associative array implementation.") - arm/IXP4xx was part of the initial repo - arm/cluster-pm-race-avoidance.txt was added by commit 7fe31d28e839 ("ARM: mcpm: introduce helpers for platform coherency exit/setup") - arm/firmware.txt was added by commit 7366b92a77fc ("ARM: Add interface for registering and calling firmware-specific operations") - arm/kernel_mode_neon.txt was added by commit 2afd0a05241d ("ARM: 7825/1: document the use of NEON in kernel mode") - arm/tcm.txt was added by commit bc581770cfdd ("ARM: 5580/2: ARM TCM (Tightly-Coupled Memory) support v3") - arm/vlocks.txt was added by commit 9762f12d3e05 ("ARM: mcpm: Add baremetal voting mutexes") - blackfin/gptimers-example.c, Makefile was added by commit 4b60779d5ea7 ("Blackfin: add an example showing how to use the gptimers API") - devicetree/usage-model.txt was added by commit 31134efc681a ("dt: Linux DT usage model documentation") - fb/api.txt was added by commit fb21c2f42879 ("fbdev: Add FOURCC-based format configuration API") - fb/sm501.txt was added by commit e6a049807105 ("video, sm501: add edid and commandline support") - fb/udlfb.txt was added by commit 96f8d864afd6 ("fbdev: move udlfb out of staging.") - filesystems/Makefile was added by commit 1e0051ae48a2 ("Documentation/fs/: split txt and source files") - filesystems/nfs/nfsd-admin-interfaces.txt was added by commit 8a4c6e19cfed ("nfsd: document kernel interfaces for nfsd configuration") - ide/warm-plug-howto.txt was added by commit f74c91413ec6 ("ide: add warm-plug support for IDE devices (take 2)") - laptops/Makefile was added by commit d49129accc21 ("Documentation/laptop/: split txt and source files") - leds/leds-blinkm.txt was added by commit b54cf35a7f65 ("LEDS: add BlinkM RGB LED driver, documentation and update MAINTAINERS") - leds/ledtrig-oneshot.txt was added by commit 5e417281cde2 ("leds: add oneshot trigger") - leds/ledtrig-transient.txt was added by commit 44e1e9f8e705 ("leds: add new transient trigger for one shot timer activation") - m68k/README.buddha was part of the initial repo - networking/LICENSE.(qla3xxx|qlcnic|qlge) was added by commits 40839129f779, c4e84bde1d59, 5a4faa873782 - networking/Makefile was added by commit 3794f3e812ef ("docsrc: build Documentation/ sources") - networking/i40evf.txt was added by commit 105bf2fe6b32 ("i40evf: add driver to kernel build system") - networking/ipsec.txt was added by commit b3c6efbc36e2 ("xfrm: Add file to document IPsec corner case") - networking/mac80211-auth-assoc-deauth.txt was added by commit 3cd7920a2be8 ("mac80211: add auth/assoc/deauth flow diagram") - networking/netlink_mmap.txt was added by commit 5683264c3981 ("netlink: add documentation for memory mapped I/O") - networking/nf_conntrack-sysctl.txt was added by commit c9f9e0e1597f ("netfilter: doc: add nf_conntrack sysctl api documentation") lan) - networking/team.txt was added by commit 3d249d4ca7d0 ("net: introduce ethernet teaming device") - networking/vxlan.txt was added by commit d342894c5d2f ("vxlan: virtual extensible lan") - power/runtime_pm.txt was added by commit 5e928f77a09a ("PM: Introduce core framework for run-time PM of I/O devices (rev. 17)") - power/charger-manager.txt was added by commit 3bb3dbbd56ea ("power_supply: Add initial Charger-Manager driver") - RCU/lockdep-splat.txt was added by commit d7bd2d68aa2e ("rcu: Document interpretation of RCU-lockdep splats") - s390/kvm.txt was added by 5ecee4b (KVM: s390: API documentation) - s390/qeth.txt was added by commit b4d72c08b358 ("qeth: bridgeport support - basic control") - scheduler/sched-bwc.txt was added by commit 88ebc08ea9f7 ("sched: Add documentation for bandwidth control") - scsi/advansys.txt was added by commit 4bd6d7f35661 ("[SCSI] advansys: Move documentation to Documentation/scsi") - scsi/bfa.txt was added by commit 1ec90174bdb4 ("[SCSI] bfa: add readme file") - scsi/bnx2fc.txt was added by commit 12b8fc10eaf4 ("[SCSI] bnx2fc: Add driver documentation") - scsi/cxgb3i.txt was added by commit c3673464ebc0 ("[SCSI] cxgb3i: Add cxgb3i iSCSI driver.") - scsi/hpsa.txt was added by commit 992ebcf14f3c ("[SCSI] hpsa: Add hpsa.txt to Documentation/scsi") - scsi/link_power_management_policy.txt was added by commit ca77329fb713 ("[libata] Link power management infrastructure") - scsi/osd.txt was added by commit 78e0c621deca ("[SCSI] osd: Documentation for OSD library") - scsi/scsi-parameter.txt was created/moved by commit 163475fb111c ("Documentation: move SCSI parameters to their own text file") - serial/driver was part of the initial repo - serial/n_gsm.txt was added by commit 323e84122ec6 ("n_gsm: add a documentation") - timers/Makefile was added by commit 3794f3e812ef ("docsrc: build Documentation/ sources") - virt/kvm/s390.txt was added by commit d9101fca3d57 ("KVM: s390: diagnose call documentation") - vm/split_page_table_lock was added by commit 49076ec2ccaf ("mm: dynamically allocate page->ptl if it cannot be embedded to struct page") - w1/slaves/w1_ds28e04 was added by commit fbf7f7b4e2ae ("w1: Add 1-wire slave device driver for DS28E04-100") - w1/masters/omap-hdq was added by commit e0a29382c6f5 ("hdq: documentation for OMAP HDQ") - x86/early-microcode.txt was added by commit 0d91ea86a895 ("x86, doc: Documentation for early microcode loading") - x86/earlyprintk.txt was added by commit a1aade478862 ("x86/doc: mini-howto for using earlyprintk=dbgp") - x86/entry_64.txt was added by commit 8b4777a4b50c ("x86-64: Document some of entry_64.S") - x86/pat.txt was added by commit d27554d874c7 ("x86: PAT documentation") Moved files - arm/kernel_user_helpers.txt was moved out of arch/arm/kernel by commit 37b8304642c7 ("ARM: kuser: move interface documentation out of the source code") - efi-stub.txt was moved out of x86/ and down into Documentation/ in commit 4172fe2f8a47 ("EFI stub documentation updates") - laptops/hpfall.c was moved out of hwmon/ and into laptops/ in commit efcfed9bad88 ("Move hp_accel to drivers/platform/x86") - commit 5616c23ad9cd ("x86: doc: move x86-generic documentation from Doc/x86/i386"): * x86/usb-legacy-support.txt * x86/boot.txt * x86/zero_page.txt - power/video_extension.txt was moved to acpi in commit 70e66e4df191 ("ACPI / video: move video_extension.txt to Documentation/acpi") Removed files (left in 00-INDEX) - memory.txt was removed by commit 00ea8990aadf ("memory.txt: remove stray information") - gpio.txt was moved to gpio/ in commit fd8e198cfcaa ("Documentation: gpiolib: document new interface") - networking/DLINK.txt was removed by commit 168e06ae26dd ("drivers/net: delete old parallel port de600/de620 drivers") - serial/hayes-esp.txt was removed by commit f53a2ade0bb9 ("tty: esp: remove broken driver") - s390/TAPE was removed by commit 9e280f669308 ("[S390] remove tape block docu") - vm/locking was removed by commit 57ea8171d2bc ("mm: documentation: remove hopelessly out-of-date locking doc") - laptops/acer-wmi.txt was remvoed by commit 020036678e81 ("acer-wmi: Delete out-of-date documentation") Typos/misc issues - rpc-server-gss.txt was added as knfsd-rpcgss.txt in commit 030d794bf498 ("SUNRPC: Use gssproxy upcall for server RPCGSS authentication.") - commit b88cf73d9278 ("net: add missing entries to Documentation/networking/00-INDEX") * generic-hdlc.txt was added as generic_hdlc.txt * spider_net.txt was added as spider-net.txt - w1/master/mxc-w1 was added as mxc_w1 by commit a5fd9139f74c ("w1: add 1-wire master driver for i.MX27 / i.MX31") - s390/zfcpdump.txt was added as zfcpdump by commit 6920c12a407e ("[S390] Add Documentation/s390/00-INDEX.") Signed-off-by: Henrik Austad <henrik@austad.us> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [rcu bits] Acked-by: Rob Landley <rob@landley.net> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Rob Herring <robh+dt@kernel.org> Cc: David S. Miller <davem@davemloft.net> Cc: Mark Brown <broonie@kernel.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Gleb Natapov <gleb@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Len Brown <len.brown@intel.com> Cc: James Bottomley <JBottomley@parallels.com> Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-02-10 22:25:33 +00:00
null_blk.txt
- Null block for block-layer benchmarking.
queue-sysfs.txt
- Queue's sysfs entries
request.txt
- The members of struct request (in include/linux/blkdev.h)
stat.txt
- Block layer statistics in /sys/block/<device>/stat
switching-sched.txt
- Switching I/O schedulers at runtime
writeback_cache_control.txt
- Control of volatile write back caches