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Date: Wed, 12 Jul 2017 14:19:45 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20170712181945.GA7547@flamenco>
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Subject: Re: [Qemu-devel] [PATCH 03/22] cputlb: bring back tlb_flush_count
 under !TLB_DEBUG
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To: Alex =?iso-8859-1?Q?Benn=E9e?= <alex.bennee@linaro.org>
Cc: qemu-devel@nongnu.org, Richard Henderson <rth@twiddle.net>

On Wed, Jul 12, 2017 at 14:26:36 +0100, Alex Bennée wrote:
> Emilio G. Cota <cota@braap.org> writes:
(snip)
> > This patch does the latter by embedding tlb_flush_count in CPUArchState.
> > The global count is then easily obtained by iterating over the CPU list.
> >
> > Signed-off-by: Emilio G. Cota <cota@braap.org>
> 
> As it actually fixes unintentional breakage:
> 
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> 
> That said I'm not sure if this number alone is helpful given the range
> of flushes we have. Really from a performance point of view we should
> differentiate between inline per-vCPU flushes as well as the cross-vCPU
> flushes of both asynchronus and synced varieties.
> 
> I had a go at this using QEMUs tracing infrastructure:
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg04076.html
> 
> But I guess the ideal way would be something that both keeps counters
> and optionally enable tracepoints.

Yeah the counters in my patch are there to fix the breakage while
not hurting scalability in MTTCG.

Having those counters always on + the tracers in your patchset
for more detailed info seems reasonable to me.

Maybe it's time to push to get those tracers changes in?

		Emilio