Re: [Qemu-devel] [PATCH for-2.8 v1 00/60] Modular build of trace event files

[Daniel P. Berrange]

On Thu, Sep 08, 2016 at 03:23:26PM +0200, Lluís Vilanova wrote:
> Daniel P Berrange writes:
> 
> > I previously split the global trace-events file up into one file
> > per-subdirectory to avoid merge conflict hell.
> [...]
> 
> Sorry, I could not find the message where the infrastructure is modified to
> provide this. But I think there's a more efficient way to provide modular
> auto-generated tracing code without the hierarchical indexing you proposed.

[snip]

>   struct TraceEvent ___trace_events[] = {
>       {
>           .name = "eventname",
>           .sstate = 1,
>           .dstate = ___trace_eventname_dstate;
>       }
>   }
> 
>   TraceEvent *TRACE_EVENTNAME = &___trace_events[...];

Life would be simpler if we had the 'bool dstate' as part of the
TraceEvent struct, but doing so would essentially be reverting this
previous change:

  commit 585ec7273e6fdab902b2128bc6c2a8136aafef04
  Author: Paolo Bonzini <address@hidden>
  Date:   Wed Oct 28 07:06:27 2015 +0100

    trace: track enabled events in a separate array
    
    This is more cache friendly on the fast path, where we already have
    the event id available.

I asked Paolo about this previously and he indicated it was a notable
performance improvement, so we can't put dstate back into the TraceEvent
struct :-(

Regards,
Daniel
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