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2011-06-14rcu: Use softirq to address performance regressionShaohua Li
Commit a26ac2455ffcf3(rcu: move TREE_RCU from softirq to kthread) introduced performance regression. In an AIM7 test, this commit degraded performance by about 40%. The commit runs rcu callbacks in a kthread instead of softirq. We observed high rate of context switch which is caused by this. Out test system has 64 CPUs and HZ is 1000, so we saw more than 64k context switch per second which is caused by RCU's per-CPU kthread. A trace showed that most of the time the RCU per-CPU kthread doesn't actually handle any callbacks, but instead just does a very small amount of work handling grace periods. This means that RCU's per-CPU kthreads are making the scheduler do quite a bit of work in order to allow a very small amount of RCU-related processing to be done. Alex Shi's analysis determined that this slowdown is due to lock contention within the scheduler. Unfortunately, as Peter Zijlstra points out, the scheduler's real-time semantics require global action, which means that this contention is inherent in real-time scheduling. (Yes, perhaps someone will come up with a workaround -- otherwise, -rt is not going to do well on large SMP systems -- but this patch will work around this issue in the meantime. And "the meantime" might well be forever.) This patch therefore re-introduces softirq processing to RCU, but only for core RCU work. RCU callbacks are still executed in kthread context, so that only a small amount of RCU work runs in softirq context in the common case. This should minimize ksoftirqd execution, allowing us to skip boosting of ksoftirqd for CONFIG_RCU_BOOST=y kernels. Signed-off-by: Shaohua Li <shaohua.li@intel.com> Tested-by: "Alex,Shi" <alex.shi@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-05-06rcu: move TREE_RCU from softirq to kthreadPaul E. McKenney
If RCU priority boosting is to be meaningful, callback invocation must be boosted in addition to preempted RCU readers. Otherwise, in presence of CPU real-time threads, the grace period ends, but the callbacks don't get invoked. If the callbacks don't get invoked, the associated memory doesn't get freed, so the system is still subject to OOM. But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit moves the callback invocations to a kthread, which can be boosted easily. Also add comments and properly synchronized all accesses to rcu_cpu_kthread_task, as suggested by Lai Jiangshan. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2010-10-21tracing: Cleanup the convoluted softirq tracepointsThomas Gleixner
With the addition of trace_softirq_raise() the softirq tracepoint got even more convoluted. Why the tracepoints take two pointers to assign an integer is beyond my comprehension. But adding an extra case which treats the first pointer as an unsigned long when the second pointer is NULL including the back and forth type casting is just horrible. Convert the softirq tracepoints to take a single unsigned int argument for the softirq vector number and fix the call sites. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> LKML-Reference: <alpine.LFD.2.00.1010191428560.6815@localhost6.localdomain6> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: mathieu.desnoyers@efficios.com Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org>
2010-09-07irq: Add tracepoint to softirq_raiseLai Jiangshan
Add a tracepoint for tracing when softirq action is raised. This and the existing tracepoints complete softirq's tracepoints: softirq_raise, softirq_entry and softirq_exit. And when this tracepoint is used in combination with the softirq_entry tracepoint we can determine the softirq raise latency. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Neil Horman <nhorman@tuxdriver.com> Cc: David Miller <davem@davemloft.net> Cc: Kaneshige Kenji <kaneshige.kenji@jp.fujitsu.com> Cc: Izumo Taku <izumi.taku@jp.fujitsu.com> Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Scott Mcmillan <scott.a.mcmillan@intel.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> LKML-Reference: <4C724298.4050509@jp.fujitsu.com> [ factorize softirq events with DECLARE_EVENT_CLASS ] Signed-off-by: Koki Sanagi <sanagi.koki@jp.fujitsu.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
2009-11-26tracing: Convert softirq events to DEFINE_EVENTLi Zefan
Use DECLARE_EVENT_CLASS to remove duplicate code: text data bss dec hex filename 12781 952 36 13769 35c9 kernel/softirq.o.old 11981 952 32 12965 32a5 kernel/softirq.o Two events are converted: softirq: softirq_entry, softirq_exit No change in functionality. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> LKML-Reference: <4B0E287F.4030708@cn.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-15events: Harmonize event field names and print output namesIngo Molnar
Now that we can filter based on fields via perf record, people will start using filter expressions and will expect them to be obvious. The primary way to see which fields are available is by looking at the trace output, such as: gcc-18676 [000] 343.011728: irq_handler_entry: irq=0 handler=timer cc1-18677 [000] 343.012727: irq_handler_entry: irq=0 handler=timer cc1-18677 [000] 343.032692: irq_handler_entry: irq=0 handler=timer cc1-18677 [000] 343.033690: irq_handler_entry: irq=0 handler=timer cc1-18677 [000] 343.034687: irq_handler_entry: irq=0 handler=timer cc1-18677 [000] 343.035686: irq_handler_entry: irq=0 handler=timer cc1-18677 [000] 343.036684: irq_handler_entry: irq=0 handler=timer While 'irq==0' filters work, the 'handler==<x>' filter expression does not work: $ perf record -R -f -a -e irq:irq_handler_entry --filter handler=timer sleep 1 Error: failed to set filter with 22 (Invalid argument) The problem is that while an 'irq' field exists and is recognized as a filter field - 'handler' does not exist - its name is 'name' in the output. To solve this, we need to synchronize the printout and the field names, wherever possible. In cases where the printout prints a non-field, we enclose that information in square brackets, such as: perf-1380 [013] 724.903505: softirq_exit: vec=9 [action=RCU] perf-1380 [013] 724.904482: softirq_exit: vec=1 [action=TIMER] This way users can use filter expressions more intuitively: all fields that show up as 'primary' (non-bracketed) information is filterable. This patch harmonizes the field names for all irq, bkl, power, sched and timer events. We might in fact think about dropping the print format bit of generic tracepoints altogether, and just print the fields that are being recorded. Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Tom Zanussi <tzanussi@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-09-17softirq: add BLOCK_IOPOLL to softirq_to_nameLi Zefan
With BLOCK_IOPOLL_SOFTIRQ added, softirq_to_name[] and show_softirq_name() needs to be updated. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> LKML-Reference: <4AB20398.8070209@cn.fujitsu.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-07-13tracing/events: Move TRACE_SYSTEM outside of include guardLi Zefan
If TRACE_INCLDUE_FILE is defined, <trace/events/TRACE_INCLUDE_FILE.h> will be included and compiled, otherwise it will be <trace/events/TRACE_SYSTEM.h> So TRACE_SYSTEM should be defined outside of #if proctection, just like TRACE_INCLUDE_FILE. Imaging this scenario: #include <trace/events/foo.h> -> TRACE_SYSTEM == foo ... #include <trace/events/bar.h> -> TRACE_SYSTEM == bar ... #define CREATE_TRACE_POINTS #include <trace/events/foo.h> -> TRACE_SYSTEM == bar !!! and then bar.h will be included and compiled. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> LKML-Reference: <4A5A9CF1.2010007@cn.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-06-02tracing: remove redundant SOFTIRQ from softirq event tracesSteven Rostedt
After converting the softirq tracer to use te flags options, this caused a regression with the name. Since the flag was used directly it was printed out (i.e. HRTIMER_SOFTIRQ). This patch only shows the softirq name without the SOFTIRQ part. [ Impact: fix regression of output from softirq events ] Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-05-26tracing: convert irq events to use __print_symbolicSteven Rostedt
The recording of the names at trace time is inefficient. This patch implements the softirq event recording to only record the vector and then use the __print_symbolic interface to print out the names. [ Impact: faster recording of softirq events ] Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
2009-05-01tracing: add irq tracepoint documentationJason Baron
Document irqs for the newly created docbook. [ Impact: add documentation ] Signed-off-by: Jason Baron <jbaron@redhat.com> Acked-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: akpm@linux-foundation.org Cc: rostedt@goodmis.org Cc: fweisbec@gmail.com Cc: mathieu.desnoyers@polymtl.ca Cc: wcohen@redhat.com LKML-Reference: <73ff42be3420157667ec548e9b0e409c3cfad05f.1241107197.git.jbaron@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-04-24tracing/irq: convert irq traces to use TRACE_EVENT macroSteven Rostedt
The TRACE_FORMAT will soon be deprecated. This patch converts it to the TRACE_EVENT macro. Note, this change should also speed up the tracing. [ Impact: remove a user of deprecated TRACE_FORMAT ] Cc: Jason Baron <jbaron@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-04-15tracing/events: move trace point headers into include/trace/eventsSteven Rostedt
Impact: clean up Create a sub directory in include/trace called events to keep the trace point headers in their own separate directory. Only headers that declare trace points should be defined in this directory. Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Neil Horman <nhorman@tuxdriver.com> Cc: Zhao Lei <zhaolei@cn.fujitsu.com> Cc: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro> Cc: Pekka Enberg <penberg@cs.helsinki.fi> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>