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Author SHA1 Message Date
Paul E. McKenney
ae91aa0adb rcu: Remove debugfs tracing 
RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness.  This commit therefore removes
RCU's debugfs tracing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 2017-06-08 18:52:43 -07:00
Paul E. McKenney
5f0d5a3ae7 mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU 
A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section.  Of course, that is not the
case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.

However, there is a phrase for this, namely "type safety".  This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]
Acked-by: David Rientjes <rientjes@google.com>
 2017-04-18 11:42:36 -07:00
Paul E. McKenney
b4c5bf3534 documentation: Record rcu_dereference() value mishandling 
Recent LKML discussings (see http://lwn.net/Articles/586838/ and
http://lwn.net/Articles/588300/ for the LWN writeups) brought out
some ways of misusing the return value from rcu_dereference() that
are not necessarily completely intuitive.  This commit therefore
documents what can and cannot safely be done with these values.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
 2014-04-29 08:38:33 -07:00
Henrik Austad
3cf8ca1c25 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Some of the 00-INDEX files are somewhat outdated and some folders does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  Only outdated (with the notably exception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 16:01:40 -08:00
Paul E. McKenney
a00e0d714f rcu: Remove conditional compilation for RCU CPU stall warnings 
The RCU CPU stall warnings can now be controlled using the
rcu_cpu_stall_suppress boot-time parameter or via the same parameter
from sysfs.  There is therefore no longer any reason to have
kernel config parameters for this feature.  This commit therefore
removes the RCU_CPU_STALL_DETECTOR and RCU_CPU_STALL_DETECTOR_RUNNABLE
kernel config parameters.  The RCU_CPU_STALL_TIMEOUT parameter remains
to allow the timeout to be tuned and the RCU_CPU_STALL_VERBOSE parameter
remains to allow task-stall information to be suppressed if desired.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
 2011-05-05 23:16:54 -07:00
Paul E. McKenney
c598a070bc rcu: Documentation update for CONFIG_PROVE_RCU 
Adds a lockdep.txt file and updates checklist.txt and
whatisRCU.txt to reflect the new lockdep-enabled capabilities of
RCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-13-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
 2010-02-25 10:34:53 +01:00
Paul E. McKenney
4c54005ca4 rcu: 1Q2010 update for RCU documentation 
Add expedited functions.  Review documentation and update
obsolete verbiage.  Also fix the advice for the RCU CPU-stall
kernel configuration parameter, and document RCU CPU-stall
warnings.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12635142581866-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
 2010-01-16 10:25:22 +01:00
Linus Torvalds
1df2d017fe Merge branch 'docs-next' of git://git.lwn.net/linux-2.6 
* 'docs-next' of git://git.lwn.net/linux-2.6:
  Fix a typo in the development process document.
  Document handling of bad memory
  Document RCU and unloadable modules
 2009-01-08 15:52:13 -08:00
Paul E. McKenney
64db4cfff9 "Tree RCU": scalable classic RCU implementation 
This patch fixes a long-standing performance bug in classic RCU that
results in massive internal-to-RCU lock contention on systems with
more than a few hundred CPUs.  Although this patch creates a separate
flavor of RCU for ease of review and patch maintenance, it is intended
to replace classic RCU.

This patch still handles stress better than does mainline, so I am still
calling it ready for inclusion.  This patch is against the -tip tree.
Nevertheless, experience on an actual 1000+ CPU machine would still be
most welcome.

Most of the changes noted below were found while creating an rcutiny
(which should permit ejecting the current rcuclassic) and while doing
detailed line-by-line documentation.

Updates from v9 (http://lkml.org/lkml/2008/12/2/334):

o	Fixes from remainder of line-by-line code walkthrough,
	including comment spelling, initialization, undesirable
	narrowing due to type conversion, removing redundant memory
	barriers, removing redundant local-variable initialization,
	and removing redundant local variables.

	I do not believe that any of these fixes address the CPU-hotplug
	issues that Andi Kleen was seeing, but please do give it a whirl
	in case the machine is smarter than I am.

	A writeup from the walkthrough may be found at the following
	URL, in case you are suffering from terminal insomnia or
	masochism:

	http://www.kernel.org/pub/linux/kernel/people/paulmck/tmp/rcutree-walkthrough.2008.12.16a.pdf

o	Made rcutree tracing use seq_file, as suggested some time
	ago by Lai Jiangshan.

o	Added a .csv variant of the rcudata debugfs trace file, to allow
	people having thousands of CPUs to drop the data into
	a spreadsheet.	Tested with oocalc and gnumeric.  Updated
	documentation to suit.

Updates from v8 (http://lkml.org/lkml/2008/11/15/139):

o	Fix a theoretical race between grace-period initialization and
	force_quiescent_state() that could occur if more than three
	jiffies were required to carry out the grace-period
	initialization.  Which it might, if you had enough CPUs.

o	Apply Ingo's printk-standardization patch.

o	Substitute local variables for repeated accesses to global
	variables.

o	Fix comment misspellings and redundant (but harmless) increments
	of ->n_rcu_pending (this latter after having explicitly added it).

o	Apply checkpatch fixes.

Updates from v7 (http://lkml.org/lkml/2008/10/10/291):

o	Fixed a number of problems noted by Gautham Shenoy, including
	the cpu-stall-detection bug that he was having difficulty
	convincing me was real.  ;-)

o	Changed cpu-stall detection to wait for ten seconds rather than
	three in order to reduce false positive, as suggested by Ingo
	Molnar.

o	Produced a design document (http://lwn.net/Articles/305782/).
	The act of writing this document uncovered a number of both
	theoretical and "here and now" bugs as noted below.

o	Fix dynticks_nesting accounting confusion, simplify WARN_ON()
	condition, fix kerneldoc comments, and add memory barriers
	in dynticks interface functions.

o	Add more data to tracing.

o	Remove unused "rcu_barrier" field from rcu_data structure.

o	Count calls to rcu_pending() from scheduling-clock interrupt
	to use as a surrogate timebase should jiffies stop counting.

o	Fix a theoretical race between force_quiescent_state() and
	grace-period initialization.  Yes, initialization does have to
	go on for some jiffies for this race to occur, but given enough
	CPUs...

Updates from v6 (http://lkml.org/lkml/2008/9/23/448):

o	Fix a number of checkpatch.pl complaints.

o	Apply review comments from Ingo Molnar and Lai Jiangshan
	on the stall-detection code.

o	Fix several bugs in !CONFIG_SMP builds.

o	Fix a misspelled config-parameter name so that RCU now announces
	at boot time if stall detection is configured.

o	Run tests on numerous combinations of configurations parameters,
	which after the fixes above, now build and run correctly.

Updates from v5 (http://lkml.org/lkml/2008/9/15/92, bad subject line):

o	Fix a compiler error in the !CONFIG_FANOUT_EXACT case (blew a
	changeset some time ago, and finally got around to retesting
	this option).

o	Fix some tracing bugs in rcupreempt that caused incorrect
	totals to be printed.

o	I now test with a more brutal random-selection online/offline
	script (attached).  Probably more brutal than it needs to be
	on the people reading it as well, but so it goes.

o	A number of optimizations and usability improvements:

	o	Make rcu_pending() ignore the grace-period timeout when
		there is no grace period in progress.

	o	Make force_quiescent_state() avoid going for a global
		lock in the case where there is no grace period in
		progress.

	o	Rearrange struct fields to improve struct layout.

	o	Make call_rcu() initiate a grace period if RCU was
		idle, rather than waiting for the next scheduling
		clock interrupt.

	o	Invoke rcu_irq_enter() and rcu_irq_exit() only when
		idle, as suggested by Andi Kleen.  I still don't
		completely trust this change, and might back it out.

	o	Make CONFIG_RCU_TRACE be the single config variable
		manipulated for all forms of RCU, instead of the prior
		confusion.

	o	Document tracing files and formats for both rcupreempt
		and rcutree.

Updates from v4 for those missing v5 given its bad subject line:

o	Separated dynticks interface so that NMIs and irqs call separate
	functions, greatly simplifying it.  In particular, this code
	no longer requires a proof of correctness.  ;-)

o	Separated dynticks state out into its own per-CPU structure,
	avoiding the duplicated accounting.

o	The case where a dynticks-idle CPU runs an irq handler that
	invokes call_rcu() is now correctly handled, forcing that CPU
	out of dynticks-idle mode.

o	Review comments have been applied (thank you all!!!).
	For but one example, fixed the dynticks-ordering issue that
	Manfred pointed out, saving me much debugging.  ;-)

o	Adjusted rcuclassic and rcupreempt to handle dynticks changes.

Attached is an updated patch to Classic RCU that applies a hierarchy,
greatly reducing the contention on the top-level lock for large machines.
This passes 10-hour concurrent rcutorture and online-offline testing on
128-CPU ppc64 without dynticks enabled, and exposes some timekeeping
bugs in presence of dynticks (exciting working on a system where
"sleep 1" hangs until interrupted...), which were fixed in the
2.6.27 kernel.  It is getting more reliable than mainline by some
measures, so the next version will be against -tip for inclusion.
See also Manfred Spraul's recent patches (or his earlier work from
2004 at http://marc.info/?l=linux-kernel&m=108546384711797&w=2).
We will converge onto a common patch in the fullness of time, but are
currently exploring different regions of the design space.  That said,
I have already gratefully stolen quite a few of Manfred's ideas.

This patch provides CONFIG_RCU_FANOUT, which controls the bushiness
of the RCU hierarchy.  Defaults to 32 on 32-bit machines and 64 on
64-bit machines.  If CONFIG_NR_CPUS is less than CONFIG_RCU_FANOUT,
there is no hierarchy.  By default, the RCU initialization code will
adjust CONFIG_RCU_FANOUT to balance the hierarchy, so strongly NUMA
architectures may choose to set CONFIG_RCU_FANOUT_EXACT to disable
this balancing, allowing the hierarchy to be exactly aligned to the
underlying hardware.  Up to two levels of hierarchy are permitted
(in addition to the root node), allowing up to 16,384 CPUs on 32-bit
systems and up to 262,144 CPUs on 64-bit systems.  I just know that I
am going to regret saying this, but this seems more than sufficient
for the foreseeable future.  (Some architectures might wish to set
CONFIG_RCU_FANOUT=4, which would limit such architectures to 64 CPUs.
If this becomes a real problem, additional levels can be added, but I
doubt that it will make a significant difference on real hardware.)

In the common case, a given CPU will manipulate its private rcu_data
structure and the rcu_node structure that it shares with its immediate
neighbors.  This can reduce both lock and memory contention by multiple
orders of magnitude, which should eliminate the need for the strange
manipulations that are reported to be required when running Linux on
very large systems.

Some shortcomings:

o	More bugs will probably surface as a result of an ongoing
	line-by-line code inspection.

	Patches will be provided as required.

o	There are probably hangs, rcutorture failures, &c.  Seems
	quite stable on a 128-CPU machine, but that is kind of small
	compared to 4096 CPUs.  However, seems to do better than
	mainline.

	Patches will be provided as required.

o	The memory footprint of this version is several KB larger
	than rcuclassic.

	A separate UP-only rcutiny patch will be provided, which will
	reduce the memory footprint significantly, even compared
	to the old rcuclassic.  One such patch passes light testing,
	and has a memory footprint smaller even than rcuclassic.
	Initial reaction from various embedded guys was "it is not
	worth it", so am putting it aside.

Credits:

o	Manfred Spraul for ideas, review comments, and bugs spotted,
	as well as some good friendly competition.  ;-)

o	Josh Triplett, Ingo Molnar, Peter Zijlstra, Mathieu Desnoyers,
	Lai Jiangshan, Andi Kleen, Andy Whitcroft, and Andrew Morton
	for reviews and comments.

o	Thomas Gleixner for much-needed help with some timer issues
	(see patches below).

o	Jon M. Tollefson, Tim Pepper, Andrew Theurer, Jose R. Santos,
	Andy Whitcroft, Darrick Wong, Nishanth Aravamudan, Anton
	Blanchard, Dave Kleikamp, and Nathan Lynch for keeping machines
	alive despite my heavy abuse^Wtesting.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
 2008-12-18 21:56:04 +01:00
Paul E. McKenney
1c12757c56 Document RCU and unloadable modules 
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
 2008-12-03 15:58:01 -07:00
Rob Landley
e54e54a94c Add Documentation/RCU/00-Index 
Add Documentation/RCU/00-INDEX

Signed-off-by: Rob Landley <rob@landley.net>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2007-10-17 08:43:07 -07:00