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Fix a number of kernel-doc entries for header files in include/linux by
making sure they begin with the appropriate '/**' notation and use @var
notation.
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Introduce a round_jiffies() function as well as a round_jiffies_relative()
function. These functions round a jiffies value to the next whole second.
The primary purpose of this rounding is to cause all "we don't care exactly
when" timers to happen at the same jiffy.
This avoids multiple timers firing within the second for no real reason;
with dynamic ticks these extra timers cause wakeups from deep sleep CPU
sleep states and thus waste power.
The exact wakeup moment is skewed by the cpu number, to avoid all cpus from
waking up at the exact same time (and hitting the same lock/cachelines
there)
[akpm@osdl.org: fix variable type]
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Signed-off-by: David Woodhouse <dwmw2@infradead.org>
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Commit a4a6198b80cf82eb8160603c98da218d1bd5e104:
[PATCH] tvec_bases too large for per-cpu data
introduced "struct tvec_t_base_s boot_tvec_bases" which is visible at
compile time. This means we can kill __init_timer_base and move
timer_base_s's content into tvec_t_base_s.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The nanosleep cleanup allows to remove the data field of hrtimer. The
callback function can use container_of() to get it's own data. Since the
hrtimer structure is anyway embedded in other structures, this adds no
overhead.
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This corrects some trivial errors in ARM docs and comments,
Signed-off-by: Adrian Bunk <bunk@stusta.de>
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switch itimers to a hrtimers-based implementation
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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In the recent timer rework we lost the check for an add_timer() of an
already-pending timer. That check was useful for networking, so put it back.
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Remove timer_list.magic and associated debugging code.
I originally added this when a spinlock was added to timer_list - this meant
that an all-zeroes timer became illegal and init_timer() was required.
That spinlock isn't even there any more, although timer.base must now be
initialised.
I'll keep this debugging code in -mm.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Every user of init_timer() also needs to initialize ->function and ->data
fields. This patch adds a simple setup_timer() helper for that.
The schedule_timeout() is patched as an example of usage.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Clean up timer initialization by introducing DEFINE_TIMER a'la
DEFINE_SPINLOCK. Build and boot-tested on x86. A similar patch has been
been in the -RT tree for some time.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch splits del_timer_sync() into 2 functions. The new one,
try_to_del_timer_sync(), returns -1 when it hits executing timer.
It can be used in interrupt context, or when the caller hold locks which
can prevent completion of the timer's handler.
NOTE. Currently it can't be used in interrupt context in UP case, because
->running_timer is used only with CONFIG_SMP.
Should the need arise, it is possible to kill #ifdef CONFIG_SMP in
set_running_timer(), it is cheap.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch tries to solve following problems:
1. del_timer_sync() is racy. The timer can be fired again after
del_timer_sync have checked all cpus and before it will recheck
timer_pending().
2. It has scalability problems. All cpus are scanned to determine
if the timer is running on that cpu.
With this patch del_timer_sync is O(1) and no slower than plain
del_timer(pending_timer), unless it has to actually wait for
completion of the currently running timer.
The only restriction is that the recurring timer should not use
add_timer_on().
3. The timers are not serialized wrt to itself.
If CPU_0 does mod_timer(jiffies+1) while the timer is currently
running on CPU 1, it is quite possible that local interrupt on
CPU_0 will start that timer before it finished on CPU_1.
4. The timers locking is suboptimal. __mod_timer() takes 3 locks
at once and still requires wmb() in del_timer/run_timers.
The new implementation takes 2 locks sequentially and does not
need memory barriers.
Currently ->base != NULL means that the timer is pending. In that case
->base.lock is used to lock the timer. __mod_timer also takes timer->lock
because ->base can be == NULL.
This patch uses timer->entry.next != NULL as indication that the timer is
pending. So it does __list_del(), entry->next = NULL instead of list_del()
when the timer is deleted.
The ->base field is used for hashed locking only, it is initialized
in init_timer() which sets ->base = per_cpu(tvec_bases). When the
tvec_bases.lock is locked, it means that all timers which are tied
to this base via timer->base are locked, and the base itself is locked
too.
So __run_timers/migrate_timers can safely modify all timers which could
be found on ->tvX lists (pending timers).
When the timer's base is locked, and the timer removed from ->entry list
(which means that _run_timers/migrate_timers can't see this timer), it is
possible to set timer->base = NULL and drop the lock: the timer remains
locked.
This patch adds lock_timer_base() helper, which waits for ->base != NULL,
locks the ->base, and checks it is still the same.
__mod_timer() schedules the timer on the local CPU and changes it's base.
However, it does not lock both old and new bases at once. It locks the
timer via lock_timer_base(), deletes the timer, sets ->base = NULL, and
unlocks old base. Then __mod_timer() locks new_base, sets ->base = new_base,
and adds this timer. This simplifies the code, because AB-BA deadlock is not
possible. __mod_timer() also ensures that the timer's base is not changed
while the timer's handler is running on the old base.
__run_timers(), del_timer() do not change ->base anymore, they only clear
pending flag.
So del_timer_sync() can test timer->base->running_timer == timer to detect
whether it is running or not.
We don't need timer_list->lock anymore, this patch kills it.
We also don't need barriers. del_timer() and __run_timers() used smp_wmb()
before clearing timer's pending flag. It was needed because __mod_timer()
did not lock old_base if the timer is not pending, so __mod_timer()->list_add()
could race with del_timer()->list_del(). With this patch these functions are
serialized through base->lock.
One problem. TIMER_INITIALIZER can't use per_cpu(tvec_bases). So this patch
adds global
struct timer_base_s {
spinlock_t lock;
struct timer_list *running_timer;
} __init_timer_base;
which is used by TIMER_INITIALIZER. The corresponding fields in tvec_t_base_s
struct are replaced by struct timer_base_s t_base.
It is indeed ugly. But this can't have scalability problems. The global
__init_timer_base.lock is used only when __mod_timer() is called for the first
time AND the timer was compile time initialized. After that the timer migrates
to the local CPU.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Renaud Lienhart <renaud.lienhart@free.fr>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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From: Christoph Hellwig <hch@lst.de>
timer.h is using NULL and thus needs stddef.h, without it some drivers
break on alpha.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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From: Geoff Gustafson <geoff@linux.jf.intel.com>,
"Chen, Kenneth W" <kenneth.w.chen@intel.com>,
Ingo Molnar <mingo@elte.hu>,
me.
The big-SMP guys are seeing high CPU load due to del_timer_sync()'s
inefficiencies. The callers are fs/aio.c and schedule_timeout().
We note that neither of these callers' timer handlers actually re-add the
timer - they are single-shot.
So we don't need all that complexity in del_timer_sync() - we can just run
del_timer() and if that worked we know the timer is dead.
Add del_single_shot_timer(), export it to modules and use it in AIO and
schedule_timeout().
(these numbers are for an earlier patch, but they'll be close)
Before: 32p 4p
Warm cache 29,000 505
Cold cache 37,800 1220
After: 32p 4p
Warm cache 95 88
Cold cache 1,800 140
[Measurements are CPU cycles spent in a call to del_timer_sync, the average
of 1000 calls. 32p is 16-node NUMA, 4p is SMP.]
(I cleaned up a few things and added some commentary)
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From: Martin Schwidefsky <schwidefsky@de.ibm.com>
This patch add a system control that allows to switch off the jiffies timer
interrupts while a cpu sleeps in idle. This is useful for a system running
with virtual cpus under z/VM.
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From: Ingo Molnar <mingo@elte.hu>
It unifies the functionality of add_timer() and mod_timer(), and makes any
combination of the timer API calls completely SMP-safe. del_timer() is still
not using the timer lock.
this patch fixes the only timer bug in 2.6 i'm aware of: the del_timer_sync()
+ add_timer() combination in kernel/itimer.c is buggy. This was correct code
in 2.4, because there it was safe to do an add_timer() from the timer handler
itself, parallel to a del_timer_sync().
If we want to make this safe in 2.6 too (which i think we want to) then we
have to make add_timer() almost equivalent to mod_timer(), locking-wise. And
once we are at this point i think it's much cleaner to actually make
add_timer() a variant of mod_timer(). (There's no locking cost for
add_timer(), only the cost of an extra branch. And we've removed another
commonly used function from the icache.)
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Headers touched: linux/interrupt.h, linux/sched.h, linux/timer.h
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Add some infrastructure for statically initialising timers,
use that in workqueues.
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If two CPUs run mod_timer against the same not-pending timer then they
have no locking relationship. They can both see the timer as
not-pending and they both add the timer to their cpu-local list. The
CPU which gets there second corrupts the first CPU's lists.
This was causing Dave Hansen's 8-way to oops after a couple of minutes
of specweb testing.
I believe that to fix this we need locking which is associated with the
timer itself. The easy fix is hashed spinlocking based on the timer's
address. The hard fix is a lock inside the timer itself.
It is hard because init_timer() becomes compulsory, to initialise that
spinlock. An unknown number of code paths in the kernel just wipe the
timer to all-zeroes and start using it.
I chose the hard way - it is cleaner and more idiomatic. The patch
also adds a "magic number" to the timer so we can detect when a timer
was not correctly initialised. A warning and stack backtrace is
generated and the timer is fixed up. After 16 such warnings the
warning mechanism shuts itself up until a reboot.
It took six patches to my kernel to stop the warnings from coming out.
The uninitialised timers are extremely easy to find and fix. But it
will take some time to weed them all out. Maybe we should go for
the hashed locking...
Note that the new timer->lock means that we can clean up some awkward
"oh we raced, let's try again" code in timer.c. But to do that we'd
also need to take timer->lock in the commonly-called del_timer(), so I
left it as-is.
The lock is not needed in add_timer() because concurrent
add_timer()/add_timer() and concurrent add_timer()/mod_timer() are
illegal.
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add_timer_on is like add_timer, except it takes a target CPU on which
to add the timer.
The slab code needs per-cpu timers for shrinking the per-cpu caches.
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This does a number of timer subsystem enhancements:
- simplified timer initialization, now it's the cheapest possible thing:
static inline void init_timer(struct timer_list * timer)
{
timer->base = NULL;
}
since the timer functions already did a !timer->base check this did not
have any effect on their fastpath.
- the rule from now on is that timer->base is set upon activation of the
timer, and cleared upon deactivation. This also made it possible to:
- reorganize all the timer handling code to not assume anything about
timer->entry.next and timer->entry.prev - this also removed lots of
unnecessery cleaning of these fields. Removed lots of unnecessary list
operations from the fastpath.
- simplified del_timer_sync(): it now uses del_timer() plus some simple
synchronization code. Note that this also fixes a bug: if mod_timer (or
add_timer) moves a currently executing timer to another CPU's timer
vector, then del_timer_sync() does not synchronize with the handler
properly.
- bugfix: moved run_local_timers() from scheduler_tick() into
update_process_times() .. scheduler_tick() might be called from the fork
code which will not quite have the intended effect ...
- removed the APIC-timer-IRQ shifting done on SMP, Dipankar Sarma's
testing shows no negative effects.
- cleaned up include/linux/timer.h:
- removed the timer_t typedef, and fixes up kernel/workqueue.c to use
the 'struct timer_list' name instead.
- removed unnecessery includes
- renamed the 'list' field to 'entry' (it's an entry not a list head)
- exchanged the 'function' and 'data' fields. This, besides being
more logical, also unearthed the last few remaining places that
initialized timers by assuming some given field ordering, the patch
also fixes these places. (fs/xfs/pagebuf/page_buf.c,
net/core/profile.c and net/ipv4/inetpeer.c)
- removed the defunct sync_timers(), timer_enter() and timer_exit()
prototypes.
- added docbook-style comments.
- other kernel/timer.c changes:
- base->running_timer does not have to be volatile ...
- added consistent comments to all the important functions.
- made the sync-waiting in del_timer_sync preempt- and lowpower-
friendly.
i've compiled, booted & tested the patched kernel on x86 UP and SMP. I
have tried moderately high networking load as well, to make sure the timer
changes are correct - they appear to be.
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This is the smptimers patch plus the removal of old BHs and a rewrite of
task-queue handling.
Basically with the removal of TIMER_BH i think the time is right to get
rid of old BHs forever, and to do a massive cleanup of all related
fields. The following five basic 'execution context' abstractions are
supported by the kernel:
- hardirq
- softirq
- tasklet
- keventd-driven task-queues
- process contexts
I've done the following cleanups/simplifications to task-queues:
- removed the ability to define your own task-queue, what can be done is
to schedule_task() a given task to keventd, and to flush all pending
tasks.
This is actually a quite easy transition, since 90% of all task-queue
users in the kernel used BH_IMMEDIATE - which is very similar in
functionality to keventd.
I believe task-queues should not be removed from the kernel altogether.
It's true that they were written as a candidate replacement for BHs
originally, but they do make sense in a different way: it's perhaps the
easiest interface to do deferred processing from IRQ context, in
performance-uncritical code areas. They are easier to use than
tasklets.
code that cares about performance should convert to tasklets - as the
timer code and the serial subsystem has done already. For extreme
performance softirqs should be used - the net subsystem does this.
and we can do this for 2.6 - there are only a couple of areas left after
fixing all the BH_IMMEDIATE places.
i have moved all the taskqueue handling code into kernel/context.c, and
only kept the basic 'queue a task' definitions in include/linux/tqueue.h.
I've converted three of the most commonly used BH_IMMEDIATE users:
tty_io.c, floppy.c and random.c. [random.c might need more thought
though.]
i've also cleaned up kernel/timer.c over that of the stock smptimers
patch: privatized the timer-vec definitions (nothing needs it,
init_timer() used it mistakenly) and cleaned up the code. Plus i've moved
some code around that does not belong into timer.c, and within timer.c
i've organized data and functions along functionality and further
separated the base timer code from the NTP bits.
net_bh_lock: i have removed it, since it would synchronize to nothing. The
old protocol handlers should still run on UP, and on SMP the kernel prints
a warning upon use. Alexey, is this approach fine with you?
scalable timers: i've further improved the patch ported to 2.5 by wli and
Dipankar. There is only one pending issue i can see, the question of
whether to migrate timers in mod_timer() or not. I'm quite convinced that
they should be migrated, but i might be wrong. It's a 10 lines change to
switch between migrating and non-migrating timers, we can do performance
tests later on. The current, more complex migration code is pretty fast
and has been stable under extremely high networking loads in the past 2
years, so we can immediately switch to the simpler variant if someone
proves it improves performance. (I'd say if non-migrating timers improve
Apache performance on one of the bigger NUMA boxes then the point is
proven, no further though will be needed.)
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include/linux/timer.h needs to include <linux/stddef.h>
to get the definition of NULL.
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Nobody's using it any more, kill:
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Trivial patch update against 2.5.17:
Tim Schmielau <tim@physik3.uni-rostock.de>: move jiffies from sched.h to it's own jiffies.h:
Move 'jiffies' from sched.h to their own header.
Then pull the sched.h dependency from 67 files that include sched.h for
no apparent reason other than the jiffies declaration.
Move the time_[before,after}{_eq}() macros from timer.h to jiffies.h,
since there are *no* files using them that don't also use jiffies.
Many more sched.h dependencies can be killed after capable(),
request_irq(), and free_irq() are moved out of <linux/sched.h>.
Tim Schmielau <tim@physik3.uni-rostock.de>
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- Andrea: fix races in do_wp_page, free_swap_and_cache
- me: clena up page dirty handling
- Tim Waugh: parport IRQ probing and documentation fixes
- Greg KH: USB updates
- Michael Warfield: computone driver update
- Randy Dunlap: add knowledge about some new io-apics
- Richard Henderson: alpha updates
- Trond Myklebust: make readdir xdr verify the reply packet
- Paul Mackerras: PPC update
- Jens Axboe: make cpqarray and cciss play nice with the request layer
- Massimo Dal Zotto: SMM driver for Dell Inspiron 8000
- Richard Gooch: devfs symlink deadlock fix
- Anton Altaparmakov: make NTFS compile on sparc
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- me/Al Viro: fix bdget() oops with block device modules that don't
clean up after they exit
- Alan Cox: continued merging (drivers, license tags)
- David Miller: sparc update, network fixes
- Christoph Hellwig: work around broken drivers that add a gendisk more
than once
- Jakub Jelinek: handle more ELF loading special cases
- Trond Myklebust: NFS client and lockd reclaimer cleanups/fixes
- Greg KH: USB updates
- Mikael Pettersson: sparate out local APIC / IO-APIC config options
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- Neil Brown: md cleanups/fixes
- Andrew Morton: console locking merge
- Andrea Arkangeli: major VM merge
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- Al Viro: clean up driver "invalidate_device()" mess
- Andries Brouwer: make sd.c work with USB Dane-Elec CompactFlash Card
Reader
- me: fix nasty lazy kernel page table update problem
- me: undo fork changes. Too many user-level bugs and unresolved issues.
- Peter Anvin: iso9660 cleanups
- Alan Cox: big merge
- Johannes Erdfelt: UHCI pci DMA setup fix
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