Date: Fri, 20 Oct 2017 11:31:16 -0500 From: Bret Ketchum <bcketchum@gmail.com> To: freebsd-arch@freebsd.org Subject: Re: PEBS support in hwpmc Message-ID: <CAGm6yaS8gKmSnpO5O9YKUPqyk6cpw-=grPJf8PHW5d0MGmRq8A@mail.gmail.com> In-Reply-To: <CAFMmRNyf0vDiU52kLzV01=1qrhT1Zzv6-AJCfDv1kGzH1Hwm=A@mail.gmail.com> References: <CAGm6yaRGeX0yG2OdntVQh4gvzbxhG6QboEufhw-Xj=a_UNnTHg@mail.gmail.com> <CAFMmRNyf0vDiU52kLzV01=1qrhT1Zzv6-AJCfDv1kGzH1Hwm=A@mail.gmail.com>
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PEBS records do capture callchain-like infromation. I'm most
interested (currently) with FRONTEND_RETIRED, MEM_LOAD_RETIRED and
MEM_LOAD_L3_HIT_RETIRED. Which require understanding of sub-events.
These counters can be used to differentiate the myriad of
Front-End/Back-End bound issues before drilling down to offending code
fragments.
On Fri, Oct 20, 2017 at 9:24 AM, Ryan Stone <rysto32@gmail.com> wrote:
> On Fri, Oct 20, 2017 at 7:27 AM, Bret Ketchum <bcketchum@gmail.com> wrote:
>> Without this support (or a VTune subscription) understanding
>> Front-End/Back-End bound applications running on Skylake/Kaby Lake
>> processors will be difficult at best
>
> I'm afraid that I don't know of any work related to PEBS in hwpmc.
> However, I'm curious as to why PEBS is so important on these
> architectures. My experience with hwpmc profiling has been that
> callchain information is frequently critical for understanding the
> performance characteristics and my understanding is that PEBS by
> design cannot capture that information.
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