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

[Andi Kleen]

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@xxxxxxxxx>


Thanks. That is useful.


Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>


-Andi