forked from luck/tmp_suning_uos_patched
e7e2ee89a9
In using syscall tracing by concurrent processes, the wakeup() that is called in the event commit function causes contention on the spin lock of the waitqueue. I enabled sys_enter_getuid and sys_exit_getuid tracepoints, and by running getuid_microbench from autotest in parallel I found that the contention causes exponential latency increase in the tracing path. The autotest binary getuid_microbench calls getuid() in a tight loop for the given number of iterations and measures the average time required to complete a single invocation of syscall. The patch schedules a delayed work after 2 ms once an event commit calls to wake up the trace wait_queue. This removes the delay caused by contention on spin lock in wakeup() and amortizes the wakeup() calls scheduled over the 2 ms period. In the following example, the script enables the sys_enter_getuid and sys_exit_getuid tracepoints and runs the getuid_microbench in parallel with the given number of processes. The output clearly shows the latency increase caused by contentions. $ ~/getuid.sh 1 1000000 calls in 0.720974253 s (720.974253 ns/call) $ ~/getuid.sh 2 1000000 calls in 1.166457554 s (1166.457554 ns/call) 1000000 calls in 1.168933765 s (1168.933765 ns/call) $ ~/getuid.sh 3 1000000 calls in 1.783827516 s (1783.827516 ns/call) 1000000 calls in 1.795553270 s (1795.553270 ns/call) 1000000 calls in 1.796493376 s (1796.493376 ns/call) $ ~/getuid.sh 4 1000000 calls in 4.483041796 s (4483.041796 ns/call) 1000000 calls in 4.484165388 s (4484.165388 ns/call) 1000000 calls in 4.484850762 s (4484.850762 ns/call) 1000000 calls in 4.485643576 s (4485.643576 ns/call) $ ~/getuid.sh 5 1000000 calls in 6.497521653 s (6497.521653 ns/call) 1000000 calls in 6.502000236 s (6502.000236 ns/call) 1000000 calls in 6.501709115 s (6501.709115 ns/call) 1000000 calls in 6.502124100 s (6502.124100 ns/call) 1000000 calls in 6.502936358 s (6502.936358 ns/call) After the patch, the latencies scale better. 1000000 calls in 0.728720455 s (728.720455 ns/call) 1000000 calls in 0.842782857 s (842.782857 ns/call) 1000000 calls in 0.883803135 s (883.803135 ns/call) 1000000 calls in 0.902077764 s (902.077764 ns/call) 1000000 calls in 0.902838202 s (902.838202 ns/call) 1000000 calls in 0.908896885 s (908.896885 ns/call) 1000000 calls in 0.932523515 s (932.523515 ns/call) 1000000 calls in 0.958009672 s (958.009672 ns/call) 1000000 calls in 0.986188020 s (986.188020 ns/call) 1000000 calls in 0.989771102 s (989.771102 ns/call) 1000000 calls in 0.933518391 s (933.518391 ns/call) 1000000 calls in 0.958897947 s (958.897947 ns/call) 1000000 calls in 1.031038897 s (1031.038897 ns/call) 1000000 calls in 1.089516025 s (1089.516025 ns/call) 1000000 calls in 1.141998347 s (1141.998347 ns/call) Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Michael Rubin <mrubin@google.com> Cc: David Sharp <dhsharp@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1305059241-7629-1-git-send-email-vnagarnaik@google.com Signed-off-by: Steven Rostedt <rostedt@goodmis.org> |
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| .. | ||
| blktrace.c | ||
| ftrace.c | ||
| Kconfig | ||
| Makefile | ||
| power-traces.c | ||
| ring_buffer_benchmark.c | ||
| ring_buffer.c | ||
| trace_branch.c | ||
| trace_clock.c | ||
| trace_entries.h | ||
| trace_event_perf.c | ||
| trace_events_filter.c | ||
| trace_events.c | ||
| trace_export.c | ||
| trace_functions_graph.c | ||
| trace_functions.c | ||
| trace_irqsoff.c | ||
| trace_kdb.c | ||
| trace_kprobe.c | ||
| trace_mmiotrace.c | ||
| trace_nop.c | ||
| trace_output.c | ||
| trace_output.h | ||
| trace_printk.c | ||
| trace_sched_switch.c | ||
| trace_sched_wakeup.c | ||
| trace_selftest_dynamic.c | ||
| trace_selftest.c | ||
| trace_stack.c | ||
| trace_stat.c | ||
| trace_stat.h | ||
| trace_syscalls.c | ||
| trace_workqueue.c | ||
| trace.c | ||
| trace.h | ||