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Date: Mon, 21 Mar 2016 17:51:52 +0100
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	(Peter Maydell's message of "Sun, 20 Mar 2016 19:59:55 +0000")
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Subject: Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, QEMU Developers <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>

Peter Maydell writes:

> On 20 March 2016 at 18:09, Llu=C3=ADs Vilanova <vilanova@ac.upc.edu> wrot=
e:
>> Oh! Yes, I seem to remember that code path now, I checked it a
>> really long time ago. I was assuming that whenever this event is
>> enabled at compile time, I would have to modify QEMU's TLB to store
>> the guest physical address (then used by the tracing event).

> I guess we could maybe put that into the iotlb. You definitely
> don't want it in the CPUTLBEntry struct as that one is space
> critical for performance. (If you're really lucky you can
> reconstruct the physaddr from the iotlb addr field but I suspect
> you can't.)

> Once you've decided to take the hit of keeping the paddr in the
> TLB it's probably faster to just unconditionally store it rather
> than doing a "store if trace event X enabled" test.

I meant to make the check at compile time, since we have defines to check w=
hich
events are enabled/disabled in trace-events.


> PS: you probably also want to be able to trace the MemTxAttrs
> (which tells you whether you have an S or NS access on ARM,
> among other things).

I'll keep these in mind for a separate series with extended memory info.


Thanks,
  Lluis