user/sven/linux.git/kernel/events/ring_buffer.c, branch v5.5.13

perf/aux: Allow using AUX data in perf samples

2019-11-13T10:06:14Z

AUX data can be used to annotate perf events such as performance counters or tracepoints/breakpoints by including it in sample records when PERF_SAMPLE_AUX flag is set. Such samples would be instrumental in debugging and profiling by providing, for example, a history of instruction flow leading up to the event's overflow. The implementation makes use of grouping an AUX event with all the events that wish to take samples of the AUX data, such that the former is the group leader. The samplees should also specify the desired size of the AUX sample via attr.aux_sample_size. AUX capable PMUs need to explicitly add support for sampling, because it relies on a new callback to take a snapshot of the buffer without touching the event states. Signed-off-by: Alexander Shishkin Signed-off-by: Peter Zijlstra (Intel) Cc: Arnaldo Carvalho de Melo Cc: David Ahern Cc: Jiri Olsa Cc: Linus Torvalds Cc: Mark Rutland Cc: Namhyung Kim Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: adrian.hunter@intel.com Cc: mathieu.poirier@linaro.org Link: https://lkml.kernel.org/r/20191025140835.53665-2-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar

perf/ring_buffer: Matching the memory allocate and free, in rb_alloc()

2019-10-17T19:31:55Z

Currently perf_mmap_alloc_page() is used to allocate memory in rb_alloc(), but using free_page() to free memory in the failure path. It's better to use perf_mmap_free_page() instead. Signed-off-by: Yunfeng Ye Signed-off-by: Peter Zijlstra (Intel) Cc: Cc: Cc: Cc: Cc: Cc: Link: https://lkml.kernel.org/r/575c7e8c-90c7-4e3a-b41d-f894d8cdbd7f@huawei.com

perf/ring_buffer: Modify the parameter type of perf_mmap_free_page()

2019-10-17T19:31:55Z

In perf_mmap_free_page(), the unsigned long type is converted to the pointer type, but where the call is made, the pointer type is converted to the unsigned long type. There is no need to do these operations. Modify the parameter type of perf_mmap_free_page() to pointer type. Signed-off-by: Yunfeng Ye Signed-off-by: Peter Zijlstra (Intel) Cc: Cc: Cc: Cc: Cc: Cc: Link: https://lkml.kernel.org/r/e6ae3f0c-d04c-50f9-544a-aee3b30330cd@huawei.com

perf/ring-buffer: Use regular variables for nesting

2019-05-24T07:00:11Z

While the IRQ/NMI will nest, the nest-count will be invariant over the actual exception, since it will decrement equal to increment. This means we can -- carefully -- use a regular variable since the typical LOAD-STORE race doesn't exist (similar to preempt_count). This optimizes the ring-buffer for all LOAD-STORE architectures, since they need to use atomic ops to implement local_t. Suggested-by: Alexander Shishkin Signed-off-by: Peter Zijlstra (Intel) Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: acme@kernel.org Cc: mark.rutland@arm.com Cc: namhyung@kernel.org Cc: yabinc@google.com Link: http://lkml.kernel.org/r/20190517115418.481392777@infradead.org Signed-off-by: Ingo Molnar

perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data

2019-05-24T07:00:11Z

We must use {READ,WRITE}_ONCE() on rb->user_page data such that concurrent usage will see whole values. A few key sites were missing this. Suggested-by: Yabin Cui Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: acme@kernel.org Cc: mark.rutland@arm.com Cc: namhyung@kernel.org Fixes: 7b732a750477 ("perf_counter: new output ABI - part 1") Link: http://lkml.kernel.org/r/20190517115418.394192145@infradead.org Signed-off-by: Ingo Molnar

perf/ring_buffer: Add ordering to rb->nest increment

2019-05-24T07:00:10Z

Similar to how decrementing rb->next too early can cause data_head to (temporarily) be observed to go backward, so too can this happen when we increment too late. This barrier() ensures the rb->head load happens after the increment, both the one in the 'goto again' path, as the one from perf_output_get_handle() -- albeit very unlikely to matter for the latter. Suggested-by: Yabin Cui Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: acme@kernel.org Cc: mark.rutland@arm.com Cc: namhyung@kernel.org Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables") Link: http://lkml.kernel.org/r/20190517115418.309516009@infradead.org Signed-off-by: Ingo Molnar

perf/ring_buffer: Fix exposing a temporarily decreased data_head

2019-05-24T07:00:10Z

In perf_output_put_handle(), an IRQ/NMI can happen in below location and write records to the same ring buffer: ... local_dec_and_test(&rb->nest) ... <-- an IRQ/NMI can happen here rb->user_page->data_head = head; ... In this case, a value A is written to data_head in the IRQ, then a value B is written to data_head after the IRQ. And A > B. As a result, data_head is temporarily decreased from A to B. And a reader may see data_head < data_tail if it read the buffer frequently enough, which creates unexpected behaviors. This can be fixed by moving dec(&rb->nest) to after updating data_head, which prevents the IRQ/NMI above from updating data_head. [ Split up by peterz. ] Signed-off-by: Yabin Cui Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: mark.rutland@arm.com Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables") Link: http://lkml.kernel.org/r/20190517115418.224478157@infradead.org Signed-off-by: Ingo Molnar

perf/ring_buffer: Fix AUX software double buffering

2019-05-03T10:46:10Z

This recent commit: 5768402fd9c6e87 ("perf/ring_buffer: Use high order allocations for AUX buffers optimistically") overlooked the fact that the previous one page granularity of the AUX buffer provided an implicit double buffering capability to the PMU driver, which went away when the entire buffer became one high-order page. Always make the full-trace mode AUX allocation at least two-part to preserve the previous behavior and allow the implicit double buffering to continue. Reported-by: Ammy Yi Signed-off-by: Alexander Shishkin Acked-by: Peter Zijlstra Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: adrian.hunter@intel.com Fixes: 5768402fd9c6e87 ("perf/ring_buffer: Use high order allocations for AUX buffers optimistically") Link: http://lkml.kernel.org/r/20190503085536.24119-2-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar

perf/ring_buffer: Fix AUX record suppression

2019-04-16T10:13:57Z

The following commit: 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records") has an unintended side-effect of also suppressing all AUX records with no flags and non-zero size, so all the regular records in the full trace mode. This breaks some use cases for people. Fix this by restoring "regular" AUX records. Reported-by: Ben Gainey Tested-by: Ben Gainey Signed-off-by: Alexander Shishkin Signed-off-by: Peter Zijlstra (Intel) Cc: Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Fixes: 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records") Link: https://lkml.kernel.org/r/20190329091338.29999-1-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar

perf/core: Fix perf_event_disable_inatomic() race

2019-04-12T06:55:55Z

Thomas-Mich Richter reported he triggered a WARN()ing from event_function_local() on his s390. The problem boils down to: CPU-A CPU-B perf_event_overflow() perf_event_disable_inatomic() @pending_disable = 1 irq_work_queue(); sched-out event_sched_out() @pending_disable = 0 sched-in perf_event_overflow() perf_event_disable_inatomic() @pending_disable = 1; irq_work_queue(); // FAILS irq_work_run() perf_pending_event() if (@pending_disable) perf_event_disable_local(); // WHOOPS The problem exists in generic, but s390 is particularly sensitive because it doesn't implement arch_irq_work_raise(), nor does it call irq_work_run() from it's PMU interrupt handler (nor would that be sufficient in this case, because s390 also generates perf_event_overflow() from pmu::stop). Add to that the fact that s390 is a virtual architecture and (virtual) CPU-A can stall long enough for the above race to happen, even if it would self-IPI. Adding a irq_work_sync() to event_sched_in() would work for all hardare PMUs that properly use irq_work_run() but fails for software PMUs. Instead encode the CPU number in @pending_disable, such that we can tell which CPU requested the disable. This then allows us to detect the above scenario and even redirect the IPI to make up for the failed queue. Reported-by: Thomas-Mich Richter Tested-by: Thomas Richter Signed-off-by: Peter Zijlstra (Intel) Acked-by: Mark Rutland Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Heiko Carstens Cc: Hendrik Brueckner Cc: Jiri Olsa Cc: Kees Cook Cc: Linus Torvalds Cc: Martin Schwidefsky Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar