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[Qemu-devel] [PATCH v5 0/7] trace: [tcg] Optimize per-vCPU tracing state
From: |
Lluís Vilanova |
Subject: |
[Qemu-devel] [PATCH v5 0/7] trace: [tcg] Optimize per-vCPU tracing states with separate TB caches |
Date: |
Wed, 28 Dec 2016 15:07:42 +0100 |
User-agent: |
StGit/0.17.1-dirty |
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 <address@hidden>
---
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: address@hidden
Cc: Stefan Hajnoczi <address@hidden>
Cc: Eduardo Habkost <address@hidden>
Cc: Eric Blake <address@hidden>
- [Qemu-devel] [PATCH v5 0/7] trace: [tcg] Optimize per-vCPU tracing states with separate TB caches,
Lluís Vilanova <=
- [Qemu-devel] [PATCH v5 1/7] exec: [tcg] Refactor flush of per-CPU virtual TB cache, Lluís Vilanova, 2016/12/28
- [Qemu-devel] [PATCH v5 2/7] trace: Make trace_get_vcpu_event_count() inlinable, Lluís Vilanova, 2016/12/28
- [Qemu-devel] [PATCH v5 3/7] trace: [tcg] Delay changes to dynamic state when translating, Lluís Vilanova, 2016/12/28
- [Qemu-devel] [PATCH v5 4/7] exec: [tcg] Use different TBs according to the vCPU's dynamic tracing state, Lluís Vilanova, 2016/12/28
- [Qemu-devel] [PATCH v5 5/7] trace: [tcg] Do not generate TCG code to trace dinamically-disabled events, Lluís Vilanova, 2016/12/28
- [Qemu-devel] [PATCH v5 6/7] trace: [tcg, trivial] Re-align generated code, Lluís Vilanova, 2016/12/28
- [Qemu-devel] [PATCH v5 7/7] trace: [trivial] Statically enable all guest events, Lluís Vilanova, 2016/12/28