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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Mon, 18 Jan 2016 11:50:55 +0100
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Subject: Re: [Qemu-devel] [PATCH v4 8/9] trace: [tcg] Add per-vCPU tracing
 states for events with the 'vcpu' property
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To: =?UTF-8?Q?Llu=c3=ads_Vilanova?= <vilanova@ac.upc.edu>, qemu-devel@nongnu.org
Cc: Eduardo Habkost <ehabkost@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Stefan Hajnoczi <stefanha@gmail.com>, Riku Voipio <riku.voipio@iki.fi>, Markus Armbruster <armbru@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>, Blue Swirl <blauwirbel@gmail.com>, Stefan Hajnoczi <stefanha@redhat.com>, =?UTF-8?Q?Andreas_F=c3=a4rber?= <afaerber@suse.de>, Richard Henderson <rth@twiddle.net>



On 15/01/2016 17:38, Lluís Vilanova wrote:
> Each event with the 'vcpu' property gets a per-vCPU dynamic tracing state.
> 
> The set of enabled events with the 'vcpu' and 'tcg' properties is used
> to select a per-vCPU physical TB cache.  The number of events with both
> properties is used to select the number of physical TB caches, and a
> bitmap of the identifiers of such enabled events is used to select a
> physical TB cache.
> 
> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>

I may be wrong, but this patch and patches 3+5 seem overengineered.  Why
can't you just flush the TB cache entirely whenever the set of trace
events changes, independent of whether they use the vcpu attribute?
That's a very rare event.

Paolo