Optimizes tracing of events with the 'tcg' and 'vcpu' properties (e.g., memory accesses), making it feasible to statically enable them by default on all QEMU builds.
Some quick'n'dirty numbers with 400.perlbench (SPECcpu2006) on the train input (medium size - suns.pl) and the guest_mem_before event: * vanilla, statically disabled real 0m2,259s user 0m2,252s sys 0m0,004s * vanilla, statically enabled (overhead: 2.18x) real 0m4,921s user 0m4,912s sys 0m0,008s * multi-tb, statically disabled (overhead: 0.99x) [within noise range] real 0m2,228s user 0m2,216s sys 0m0,008s * multi-tb, statically enabled (overhead: 0.99x) [within noise range] real 0m2,229s user 0m2,224s sys 0m0,004s Right now, events with the 'tcg' property always generate TCG code to trace that event at guest code execution time, where the event's dynamic state is checked. This series adds a performance optimization where TCG code for events with the 'tcg' and 'vcpu' properties is not generated if the event is dynamically disabled. This optimization raises two issues: * An event can be dynamically disabled/enabled after the corresponding TCG code has been generated (i.e., a new TB with the corresponding code should be used). * Each vCPU can have a different dynamic state for the same event (i.e., tracing the memory accesses of only one process pinned to a vCPU). To handle both issues, this series integrates the dynamic tracing event state into the TB hashing function, so that vCPUs tracing different events will use separate TBs. Note that only events with the 'vcpu' property are used for hashing (as stored in the bitmap of CPUState->trace_dstate). This makes dynamic event state changes on vCPUs very efficient, since they can use TBs produced by other vCPUs while on the same event state combination (or produced by the same vCPU, earlier). Discarded alternatives: * Emitting TCG code to check if an event needs tracing, where we should still move the tracing call code to either a cold path (making tracing performance worse), or leave it inlined (making non-tracing performance worse). * Eliding TCG code only when *zero* vCPUs are tracing an event, since enabling it on a single vCPU will impact the performance of all other vCPUs that are not tracing that event. Signed-off-by: Lluís Vilanova <vilan...@ac.upc.edu> --- Changes in v5 ============= * Move define into "qemu-common.h" to allow compilation of tests. Changes in v4 ============= * Incorporate trace_dstate into the TB hashing function instead of using multiple physical TB caches [suggested by Richard Henderson]. Changes in v3 ============= * Rebase on 0737f32daf. * Do not use reserved symbol prefixes ("__") [Stefan Hajnoczi]. * Refactor trace_get_vcpu_event_count() to be inlinable. * Optimize cpu_tb_cache_set_requested() (hottest path). Changes in v2 ============= * Fix bitmap copy in cpu_tb_cache_set_apply(). * Split generated code re-alignment into a separate patch [Daniel P. Berrange]. Lluís Vilanova (7): exec: [tcg] Refactor flush of per-CPU virtual TB cache trace: Make trace_get_vcpu_event_count() inlinable trace: [tcg] Delay changes to dynamic state when translating exec: [tcg] Use different TBs according to the vCPU's dynamic tracing state trace: [tcg] Do not generate TCG code to trace dinamically-disabled events trace: [tcg,trivial] Re-align generated code trace: [trivial] Statically enable all guest events cpu-exec.c | 52 +++++++++++++++++++++++++++--- cputlb.c | 2 + include/exec/exec-all.h | 11 ++++++ include/exec/tb-hash-xx.h | 11 ++++++ include/exec/tb-hash.h | 5 ++- include/qemu-common.h | 3 ++ include/qom/cpu.h | 7 ++++ qom/cpu.c | 4 ++ scripts/tracetool/__init__.py | 1 + scripts/tracetool/backend/dtrace.py | 2 + scripts/tracetool/backend/ftrace.py | 20 ++++++------ scripts/tracetool/backend/log.py | 17 +++++----- scripts/tracetool/backend/simple.py | 2 + scripts/tracetool/backend/syslog.py | 6 ++- scripts/tracetool/backend/ust.py | 2 + scripts/tracetool/format/h.py | 24 ++++++++++---- scripts/tracetool/format/tcg_h.py | 19 +++++++++-- scripts/tracetool/format/tcg_helper_c.py | 3 +- tests/qht-bench.c | 2 + trace-events | 6 ++- trace/control-internal.h | 5 +++ trace/control-target.c | 14 +++++++- trace/control.c | 9 +---- trace/control.h | 5 ++- translate-all.c | 30 +++++++++++++---- 25 files changed, 198 insertions(+), 64 deletions(-) To: qemu-devel@nongnu.org Cc: Stefan Hajnoczi <stefa...@redhat.com> Cc: Eduardo Habkost <ehabk...@redhat.com> Cc: Eric Blake <ebl...@redhat.com>