linux-kernel - Re: [PATCH] perf intel-pt: Add a config for max loops without consuming a packet

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Date:   Wed, 7 Jul 2021 11:41:31 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf intel-pt: Add a config for max loops without
 consuming a packet

Em Thu, Jul 01, 2021 at 10:54:53AM -0700, Andi Kleen escreveu:
> 
> On 7/1/2021 10:51 AM, Adrian Hunter wrote:
> > The Intel PT decoder limits the number of unconditional branches (e.g.
> > jmps) decoded without consuming any trace packets. Generally, a loop
> > needs a conditional branch which generates a TNT packet, whereas a
> > "ret" instruction will generate a TIP or TNT packet. So exceeding
> > the limit is assumed to be a never-ending loop, which can happen if
> > there has been a decoding error putting the decoder at the wrong place in
> > the code.
> > 
> > Up until now, the limit of 10000 has been enough but some analytic
> > purposes have been reported to exceed that.
> > 
> > Increase the limit to 100000, and make it configurable via perf config
> > intel-pt.max-loops. Also amend the "Never-ending loop" message to
> > mention the configuration entry.
> > 
> > Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> 
> 
> Thanks. That is useful.
> 
> 
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>

Thanks, applied.

- Arnaldo