On Tue, Jul 04, 2017 at 10:30:13AM +0200, Lluís Vilanova wrote:
> 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. Last patch shows that overheads are completely eliminated in various
> types of benchmarks for linux-user and softmmu (overheads where up to 2x
> before).
>
>
> 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 <address@hidden>
> ---
>
> Changes in v11
> ==============
>
> * Rebase on 931892e8a6.
> * Drop patch for flushing per-CPU virtual TB cache.
> * Fix typo in comments.
> * Change documentation format in TranslationBlock.
>
>
> Changes in v10
> ==============
>
> * Replace lingering trace_get_vcpu_event_count() with
> CPU_TRACE_DSTATE_MAX_EVENTS [Emilio G. Cota].
> * Add performance results for dbt-bench [Emilio G. Cota].
>
>
> Changes in v9
> =============
>
> * Rebase on 931892e8a6.
> * Undo renaming of tb->trace_vcpu_dstate to the shorter tb->trace_ds.
> * Add measurements to commit enabling all guest events.
>
>
> Changes in v8
> =============
>
> [Emilio G. Cota]
>
> * Ported to current dev tree.
>
> * Allocate cpu->trace_dstate statically. This
> * allows us to drop the event_count inline patch.
> * simplifies and improves the performance of accessing cpu->trace_dstate:
> we just need to dereference, instead of going through bitmap_copy and
> an intermediate unsigned long.
>
> * If we try to register more CPU events than the max we support (there's a
> constant for it), drop the event and tell the user with error_report. But
> really this is a bug, since we control what CPU events are traceable. Should
> we abort() as well?
>
> * Added rth's R-b tag
>
> * Addressed my own comments:
> * rename tb->trace_vcpu_dstate to the shorter tb->trace_ds
> * use uint32_t for tb->trace_ds instead of a typedef
> * add BUILD_BUG_ON check to make sure tb->trace_ds is big enough
> * fix xxhash
>
> * Do not add trace_dstate to tb_htable_lookup, since we can grab it from
> cpu->trace_dstate.
>
> This patchset applies cleanly on top of rth's tcg-next (a01792e1e).
>
>
> Changes in v7
> =============
>
> * Fix delayed dstate changes (now uses async_run_on_cpu() as suggested by Paolo
> Bonzini).
>
> * Note to Richard: patch 4 has been adapted to the new patch 3 async callback,
> but is essentially the same.
>
>
> Changes in v6
> =============
>
> * Check hashing size error with QEMU_BUILD_BUG_ON [Richard Henderson].
>
>
> 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 (6):
> trace: Allocate cpu->trace_dstate in place
> 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 dynamically-disabled events
> trace: [tcg,trivial] Re-align generated code
> trace: [trivial] Statically enable all guest events
>
>
> accel/tcg/cpu-exec.c | 8 ++++++--
> accel/tcg/translate-all.c | 11 +++++++++--
> include/exec/exec-all.h | 3 +++
> include/exec/tb-hash-xx.h | 7 +++++--
> include/exec/tb-hash.h | 5 +++--
> include/qom/cpu.h | 12 ++++++------
> qom/cpu.c | 8 --------
> scripts/tracetool/__init__.py | 3 ++-
> scripts/tracetool/backend/dtrace.py | 4 ++--
> scripts/tracetool/backend/ftrace.py | 20 ++++++++++----------
> scripts/tracetool/backend/log.py | 19 ++++++++++---------
> scripts/tracetool/backend/simple.py | 4 ++--
> scripts/tracetool/backend/syslog.py | 6 +++---
> scripts/tracetool/backend/ust.py | 4 ++--
> scripts/tracetool/format/h.py | 26 +++++++++++++++++++-------
> scripts/tracetool/format/tcg_h.py | 21 +++++++++++++++++----
> scripts/tracetool/format/tcg_helper_c.py | 5 +++--
> tcg/tcg-runtime.c | 3 ++-
> tests/qht-bench.c | 2 +-
> trace-events | 6 +++---
> trace/control-target.c | 21 ++++++++++++++++++---
> trace/control.c | 9 ++++++++-
> trace/control.h | 3 +++
> 23 files changed, 137 insertions(+), 73 deletions(-)
>
>
> To: qemu-devel@nongnu.org
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Emilio G. Cota <cota@braap.org>
>
Thanks, applied to my tracing tree:
https://github.com/stefanha/qemu/commits/tracing
Stefan