Stefan Hajnoczi writes: > On Sun, Jul 30, 2017 at 05:08:18PM +0300, Lluís Vilanova wrote: >> The hypertrace channel allows guest code to emit events in QEMU (the host) >> using >> its tracing infrastructure (see "docs/trace.txt"). This works in both >> 'system' >> and 'user' modes, is architecture-agnostic and introduces minimal noise on >> the >> guest. >> >> See first commit for a full description, use-cases and an example. >> >> Signed-off-by: Lluís Vilanova <vilan...@ac.upc.edu> >> --- >> >> Changes in v8 >> ============= >> >> * Do not use 'seq' when there's no extra hypertrace arguments (BSD behaves >> differently for "seq 0"). >> * Fix compilation for bsd-user.
> Hi Lluís, > Any changes regarding the fundamental approach since September 2016? > Back then I had the following concerns about hypertrace for full-system > virtualization: > Going to QEMU for every guest trace event has high overhead under > virtualization. The alternative approach is recording separate traces > and merging them for analysis. This is possible with trace-cmd [1] and > LTTng [2]. > Merging traces eliminates the performance bottleneck and does not > require new paravirt interfaces or guest tracing libraries. I think it > it would be a distraction to support hypertrace for the virtualization > use case because it fundamentally has a high overhead. > I see promise in using hypertrace for TCG because it is low-overhead > when running inside the QEMU process. I'll review the patches again > with this in mind and not focus on virtualization. > [1] https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg00887.html > [2] > http://archive.eclipse.org/tracecompass/doc/stable/org.eclipse.tracecompass.doc.user/Virtual-Machine-Analysis.html > and also generic trace synchronization > > http://archive.eclipse.org/tracecompass/doc/stable/org.eclipse.tracecompass.doc.user/Trace-synchronization.html#Trace_synchronization There's been no fundamental changes since then (just the few bits listed in the v5-v8 changelog). But I'm kind of split on this one. If you want high-performance trace correlation, this will work much better for TCG than virtualization (where [1] will probably be more efficient). If you want a hook to trigger other operations (like in the docs example), I think this is the right approach. In fact, my initial interest in hypertrace was for instrumentation, so maybe this should be subsumed into the proposal of a stable instrumentation API. What do you think? Cheers, Lluis > Stefan >> Changes in v7 >> ============= >> >> * Use 'expr' instead of assuming 'bash' when generating the "emit.c" file. >> * Restore generation of trace-events-all. >> >> >> Changes in v6 >> ============= >> >> * Fix compilation errors. >> >> >> Changes in v5 >> ============= >> >> * Rebase on 5a477a7806. >> * Fix typo in "bsd-user/main.c" [Stephan Hajnoczi]. >> * Replace abort() with exit() in command-line errors [Stephan Hajnoczi]. >> * Fix alignment of data and control channels [Stephan Hajnoczi]. >> * Fix signal reflection in user-mode (SIGINT, SIGABRT, SIGSEGV) [Stephan >> Hajnoczi]. >> * Clarify semantics of hypertrace_guest_mmap_check() [Stephan Hajnoczi]. >> * Use uintptr_t instead of unsigned long in SEGV handler [Stephan Hajnoczi]. >> * Emit hypertrace's event with host-endian arguments [Stephan Hajnoczi]. >> * Enable true concurrency between user-mode guest threads by using a >> spearate control channel page per client [Stephan Hajnoczi]. >> * Remove unused PAGE_SIZE define [Stephan Hajnoczi]. >> * Submit linux kernel API module separately to Linux upstream [Stephan >> Hajnoczi]. >> * Assume guest code events are always enabled. >> >> >> Changes in v4 >> ============= >> >> * Fix typo in stap script example. >> * Fix compilation instructions in doc/hypertrace.txt. >> * Rebase on 0737f32daf. >> >> >> Changes in v3 >> ============= >> >> * Rebase on 4a58f35. >> * Remove debugging printf's. >> * Fix style issues identified by checkpatch. >> * Fix control channel mapping in guest linux module. >> * Add a short event description in "trace-events". >> * Polish documentation in 1st patch. >> >> >> Changes in v2 >> ============= >> >> * Remove unnecessary casts for g2h() [Eric Blake]. >> * Use perror() [Eric Blake]. >> * Avoid expansions in application example [Eric Blake]. >> * Add copyright in document "hypertrace.txt" [Eric Blake]. >> * Make the user-mode hypertrace invocations thread-safe [Stefan Hajnoczi]. >> * Split dynamic hypertrace configuration into a separate "config" channel. >> >> Lluís Vilanova (5): >> hypertrace: Add documentation >> hypertrace: Add tracing event "guest_hypertrace" >> hypertrace: [*-user] Add QEMU-side proxy to "guest_hypertrace" event >> hypertrace: [softmmu] Add QEMU-side proxy to "guest_hypertrace" event >> hypertrace: Add guest-side user-level library >> >> >> Makefile | 11 + >> Makefile.objs | 6 + >> bsd-user/main.c | 17 + >> bsd-user/mmap.c | 15 + >> bsd-user/qemu.h | 3 >> bsd-user/syscall.c | 34 ++- >> configure | 36 +++ >> docs/devel/tracing.txt | 3 >> docs/hypertrace.txt | 225 ++++++++++++++++++++ >> hypertrace/Makefile.objs | 25 ++ >> hypertrace/common.c | 55 +++++ >> hypertrace/common.h | 25 ++ >> hypertrace/guest/Makefile | 30 +++ >> hypertrace/guest/common.c | 301 ++++++++++++++++++++++++++ >> hypertrace/guest/qemu-hypertrace.h | 80 +++++++ >> hypertrace/softmmu.c | 237 +++++++++++++++++++++ >> hypertrace/user.c | 415 >> ++++++++++++++++++++++++++++++++++++ >> hypertrace/user.h | 71 ++++++ >> include/hw/pci/pci.h | 2 >> include/qom/cpu.h | 4 >> linux-user/main.c | 19 ++ >> linux-user/mmap.c | 16 + >> linux-user/qemu.h | 3 >> linux-user/signal.c | 12 + >> linux-user/syscall.c | 31 ++- >> rules.mak | 2 >> trace-events | 11 + >> 27 files changed, 1660 insertions(+), 29 deletions(-) >> create mode 100644 docs/hypertrace.txt >> create mode 100644 hypertrace/Makefile.objs >> create mode 100644 hypertrace/common.c >> create mode 100644 hypertrace/common.h >> create mode 100644 hypertrace/guest/Makefile >> create mode 100644 hypertrace/guest/common.c >> create mode 100644 hypertrace/guest/qemu-hypertrace.h >> create mode 100644 hypertrace/softmmu.c >> create mode 100644 hypertrace/user.c >> create mode 100644 hypertrace/user.h >> >> >> To: qemu-devel@nongnu.org >> Cc: Stefan Hajnoczi <stefa...@redhat.com> >> Cc: Eric Blake <ebl...@redhat.com> >> Cc: Luiz Capitulino <lcapitul...@redhat.com> >> Cc: Daniel P Berrange <berra...@redhat.com>
