Steven Rostedt
66a8cb95ed
ring-buffer: Add place holder recording of dropped events ...
Currently, when the ring buffer drops events, it does not record
the fact that it did so. It does inform the writer that the event
was dropped by returning a NULL event, but it does not put in any
place holder where the event was dropped.
This is not a trivial thing to add because the ring buffer mostly
runs in overwrite (flight recorder) mode. That is, when the ring
buffer is full, new data will overwrite old data.
In a produce/consumer mode, where new data is simply dropped when
the ring buffer is full, it is trivial to add the placeholder
for dropped events. When there's more room to write new data, then
a special event can be added to notify the reader about the dropped
events.
But in overwrite mode, any new write can overwrite events. A place
holder can not be inserted into the ring buffer since there never
may be room. A reader could also come in at anytime and miss the
placeholder.
Luckily, the way the ring buffer works, the read side can find out
if events were lost or not, and how many events. Everytime a write
takes place, if it overwrites the header page (the next read) it
updates a "overrun" variable that keeps track of the number of
lost events. When a reader swaps out a page from the ring buffer,
it can record this number, perfom the swap, and then check to
see if the number changed, and take the diff if it has, which would be
the number of events dropped. This can be stored by the reader
and returned to callers of the reader.
Since the reader page swap will fail if the writer moved the head
page since the time the reader page set up the swap, this gives room
to record the overruns without worrying about races. If the reader
sets up the pages, records the overrun, than performs the swap,
if the swap succeeds, then the overrun variable has not been
updated since the setup before the swap.
For binary readers of the ring buffer, a flag is set in the header
of each sub page (sub buffer) of the ring buffer. This flag is embedded
in the size field of the data on the sub buffer, in the 31st bit (the size
can be 32 or 64 bits depending on the architecture), but only 27
bits needs to be used for the actual size (less actually).
We could add a new field in the sub buffer header to also record the
number of events dropped since the last read, but this will change the
format of the binary ring buffer a bit too much. Perhaps this change can
be made if the information on the number of events dropped is considered
important enough.
Note, the notification of dropped events is only used by consuming reads
or peeking at the ring buffer. Iterating over the ring buffer does not
keep this information because the necessary data is only available when
a page swap is made, and the iterator does not swap out pages.
Cc: Robert Richter <robert.richter@amd.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: "Luis Claudio R. Goncalves" <lclaudio@uudg.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2010-03-31 22:57:04 -04:00
microblaze: Enable GCOV_PROFILE_ALL
2009-09-21 14:29:21 +02:00
Merge branch 'irq-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-26 15:09:06 -07:00
mm/pm: force GFP_NOIO during suspend/hibernation and resume
2010-03-06 11:26:26 -08:00
time: Fix accumulation bug triggered by long delay.
2010-03-23 16:41:01 +01:00
ring-buffer: Add place holder recording of dropped events
2010-03-31 22:57:04 -04:00
copy_signal() cleanup: kill taskstats_tgid_init() and acct_init_pacct()
2010-03-12 15:52:39 -08:00
Fix misspelling of "should" and "shouldn't" in comments.
2010-02-05 12:22:30 +01:00
new helper: iterate_mounts()
2010-03-03 14:07:57 -05:00
Audit: reorganize struct audit_watch to save 8 bytes
2009-09-24 03:50:25 -04:00
Lose the first argument of audit_inode_child()
2010-02-08 14:38:36 -05:00
kbuild: move bounds.h to include/generated
2009-12-12 13:08:14 +01:00
capabilities: Use RCU to protect task lookup in sys_capget
2009-12-10 09:42:48 +11:00
cgroups: remove duplicate include
2010-03-24 16:31:19 -07:00
cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time
2009-09-24 07:20:58 -07:00
kernel/cpu.c: delete deprecated definition in cpu_up()
2010-03-06 11:26:28 -08:00
cpuset: alloc nodemask_t on the heap rather than the stack
2010-03-24 16:31:21 -07:00
CRED: Fix memory leak in error handling
2010-03-30 17:15:38 +11:00
headers: taskstats_kern.h trim
2009-09-18 09:48:52 -07:00
x86: Do not free zero sized per cpu areas
2010-03-29 18:55:40 +02:00
elf coredump: add extended numbering support
2010-03-06 11:26:46 -08:00
Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-13 14:43:01 -08:00
Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-13 14:43:01 -08:00
futex: Handle futex value corruption gracefully
2010-02-03 15:13:22 +01:00
futex: Protect pid lookup in compat code with RCU
2009-12-09 14:22:14 +01:00
hrtimers: Convert to raw_spinlocks
2009-12-14 23:55:34 +01:00
softlockup: Fix hung_task_check_count sysctl
2009-11-27 06:21:57 +01:00
Merge branch 'perf/core' into perf/urgent
2010-03-04 11:47:52 +01:00
itimers: Fix racy writes to cpu_itimer fields
2009-11-18 16:32:12 +01:00
hw-breakpoints: Fix broken hw-breakpoint sample module
2009-11-10 11:23:29 +01:00
mutex: Better control mutex adaptive spinning config
2009-12-03 11:50:11 +01:00
percpu: add __percpu sparse annotations to core kernel subsystems
2010-02-17 11:17:38 +09:00
kfifo: Don't use integer as NULL pointer
2010-02-16 15:11:08 -08:00
Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-02-04 16:07:41 -08:00
kmod: fix resource leak in call_usermodehelper_pipe()
2010-01-11 09:34:04 -08:00
kprobes: Calculate the index correctly when freeing the out-of-line execution slot
2010-03-11 14:06:16 +01:00
Merge branch 'for-next' into for-linus
2010-03-08 16:55:37 +01:00
cpuset: fix the problem that cpuset_mem_spread_node() returns an offline node
2010-03-24 16:31:21 -07:00
Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-18 16:52:46 -07:00
lockdep: BFS cleanup
2009-07-24 10:53:29 +02:00
seq_file: constify seq_operations
2009-09-23 07:39:29 -07:00
elf coredump: replace ELF_CORE_EXTRA_* macros by functions
2010-03-06 11:26:45 -08:00
tracing: Fix compile error in module tracepoints when MODULE_UNLOAD not set
2010-03-31 22:56:59 -04:00
headers: remove sched.h from interrupt.h
2009-10-11 11:20:58 -07:00
locking: Implement new raw_spinlock
2009-12-14 23:55:32 +01:00
mutex: Better control mutex adaptive spinning config
2009-12-03 11:50:11 +01:00
sched: Use lockdep-based checking on rcu_dereference()
2010-02-25 10:34:26 +01:00
cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time
2009-09-24 07:20:58 -07:00
nsproxy: remove INIT_NSPROXY()
2010-03-12 15:52:40 -08:00
padata: Allocate the cpumask for the padata instance
2010-03-04 13:30:22 +08:00
panic: fix panic_timeout accuracy when running on a hypervisor
2010-03-06 11:26:33 -08:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial
2010-03-12 16:04:50 -08:00
perf: Fix unexported generic perf_arch_fetch_caller_regs
2010-03-17 12:26:49 +01:00
Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-13 14:43:01 -08:00
pid_ns: zap_pid_ns_processes: use SEND_SIG_NOINFO instead of force_sig()
2010-03-12 15:52:40 -08:00
pm_qos: clean up racy global "name" variable
2009-10-14 15:31:10 +02:00
Merge branch 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-26 15:10:38 -07:00
posix-timers.c: Don't export local functions
2010-02-05 14:54:10 +01:00
printk: avoid warning when CONFIG_PRINTK is disabled
2010-03-06 11:26:33 -08:00
kernel/profile.c: Switch /proc/irq/prof_cpu_mask to seq_file
2009-09-20 20:15:40 +02:00
ptrace: Fix ptrace_regset() comments and diagnose errors specifically
2010-02-23 13:45:26 -08:00
x86: Change range end to start+size
2010-02-10 17:47:17 -08:00
rcu: Make rcu_read_lock_bh_held() allow for disabled BH
2010-03-16 09:57:49 +01:00
rcu: Eliminate unneeded function wrapping
2009-11-22 18:58:16 +01:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu
2010-03-03 07:34:18 -08:00
rcu: Fix accelerated grace periods for last non-dynticked CPU
2010-02-27 09:53:52 +01:00
rcu: Increase RCU CPU stall timeouts if PROVE_RCU
2010-03-11 13:38:01 +01:00
rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU
2010-02-28 09:17:42 +01:00
rcu: Stop overflowing signed integers
2010-02-25 10:34:57 +01:00
splice: comparing unsigned int < 0
2010-03-06 11:26:32 -08:00
memcg: some modification to softlimit under hierarchical memory reclaim.
2009-10-01 16:11:13 -07:00
resources: add interfaces that return conflict information
2010-03-23 13:33:50 -07:00
sched: Convert pi_lock to raw_spinlock
2009-12-14 23:55:33 +01:00
rtmutes: Convert rtmutex.lock to raw_spinlock
2009-12-14 23:55:33 +01:00
sched: Use proper type in sched_getaffinity()
2010-03-17 10:48:49 +01:00
sched: Fix cpu_clock() in NMIs, on !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2009-12-15 09:04:36 +01:00
Merge branch 'for-next' into for-linus
2010-03-08 16:55:37 +01:00
sched: Convert cpupri lock to raw_spinlock
2009-12-14 23:55:33 +01:00
sched: Convert rq->lock to raw_spinlock
2009-12-14 23:55:33 +01:00
sched, rcu: Fix rcu_dereference() for RCU-lockdep
2010-03-01 09:29:58 +01:00
sched: Discard some old bits
2009-12-09 10:03:07 +01:00
sched: Remove the sched_class load_balance methods
2010-01-21 13:40:09 +01:00
Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
2010-03-13 14:46:18 -08:00
kernel core: use helpers for rlimits
2010-03-06 11:26:33 -08:00
SLOW_WORK: Move slow_work's proc file to debugfs
2009-12-01 08:20:31 -08:00
slow-work: use get_ref wrapper instead of directly calling get_ref
2010-03-29 09:13:30 -07:00
SLOW_WORK: CONFIG_SLOW_WORK_PROC should be CONFIG_SLOW_WORK_DEBUG
2010-03-29 09:14:47 -07:00
generic-ipi: Optimize accesses by using DEFINE_PER_CPU_SHARED_ALIGNED for IPI data
2010-01-18 09:02:59 +01:00
hrtimer, softirq: Fix hrtimer->softirq trampoline
2010-02-03 18:17:40 +01:00
softlockup: Stop spurious softlockup messages due to overflow
2010-03-21 19:30:13 +01:00
locking: Cleanup the name space completely
2009-12-14 23:55:33 +01:00
rcu: Introduce lockdep-based checking to RCU read-side primitives
2010-02-25 09:40:59 +01:00
percpu: add __percpu sparse annotations to core kernel subsystems
2010-02-17 11:17:38 +09:00
Add generic sys_olduname()
2010-03-12 15:52:32 -08:00
Add generic sys_ipc wrapper
2010-03-12 15:52:32 -08:00
sysctl extern cleanup: lockdep
2010-03-12 15:53:10 -08:00
Switch may_open() and break_lease() to passing O_...
2010-03-03 13:00:21 -05:00
ipv4 05/05: add sysctl to accept packets with local source addresses
2009-12-03 12:14:38 -08:00
const: struct nla_policy
2010-02-18 14:30:18 -08:00
Revert "time: Remove xtime_cache"
2009-12-22 14:10:37 -08:00
timer stats: Fix del_timer_sync() and try_to_del_timer_sync()
2010-03-12 19:11:29 +01:00
trivial: fix typo "to to" in multiple files
2009-09-21 15:14:55 +02:00
mm: clean up mm_counter
2010-03-06 11:26:23 -08:00
headers: utsname.h redux
2009-09-23 18:13:10 -07:00
core: Clean up user return notifers use of per_cpu
2009-12-02 10:22:59 +01:00
sched: Remove USER_SCHED
2010-01-21 13:40:18 +01:00
sysctl kernel: Remove binary sysctl logic
2009-11-12 02:04:55 -08:00
locking, sched: Give waitqueue spinlocks their own lockdep classes
2009-08-10 14:43:09 +02:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq
2009-12-10 09:35:44 -08:00
66a8cb95ed