From: "Steinar H. Gunderson" <sesse@google.com>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf intel-pt: Synthesize cycle events
Date: Mon, 21 Mar 2022 11:33:50 +0100 [thread overview]
Message-ID: <YjhUjotmo+kYvoNP@google.com> (raw)
In-Reply-To: <371faf0d-f794-4a2e-0a1c-9d454d7c8b12@intel.com>
On Mon, Mar 21, 2022 at 11:16:56AM +0200, Adrian Hunter wrote:
> I had another look at this and it seemed *mostly* OK for me. One change
> I would make is to subject the cycle period to the logic of the 'A' option
> (approximate IPC).
>
> So what does the 'A' option do.
>
> By default, IPC is output only when the exact number of cycles and
> instructions is known for the sample. Decoding walks instructions
> to reconstruct the control flow, so the exact number of instructions
> is known, but the cycle count (CYC packet) is only produced with
> another packet, so only indirect/async branches or the first
> conditional branch of a TNT packet.
Ah, I hadn't thought of the fact that you only get the first branch per
packet. It's a bit unfortunate for (exact) cycle counts, since I guess
TNT packets can also easily cross functions?
> So the cycle sample function looks like this:
>
> static int intel_pt_synth_cycle_sample(struct intel_pt_queue *ptq)
>
> [...]
>
> With regard to the results you got with perf report, please try:
>
> perf report --itrace=y0nse --show-total-period --stdio
>
> and see if the percentages and cycle counts for rarely executed
> functions make more sense.
I already run mostly with 0ns period, so I don't think that's it.
I tried your new version, and it's very similar to your previous one;
there are some small changes (largest is that one function goes from
2.5% to 2.2% or so), but the general gist of it is the same.
I am increasingly leaning towards that my original version is wrong
somehow, though.
By the way, I noticed that synthesized call stacks do not respect
--inline; is that on purpose? The patch seems simple enough (just
a call to add_inlines), although it exposes extreme slowness in libbfd
when run over large binaries, which I'll have to look into.
(10+ ms for each address-to-symbol lookup is rather expensive when you
have 4M samples to churn through!)
/* Steinar */
next prev parent reply other threads:[~2022-03-21 10:34 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-10 9:38 [PATCH] perf intel-pt: Synthesize cycle events Steinar H. Gunderson
2022-03-11 9:10 ` Adrian Hunter
2022-03-11 17:42 ` Steinar H. Gunderson
2022-03-14 16:24 ` Adrian Hunter
2022-03-15 10:16 ` Steinar H. Gunderson
2022-03-15 11:32 ` Adrian Hunter
2022-03-15 18:00 ` Steinar H. Gunderson
2022-03-15 20:11 ` Adrian Hunter
2022-03-16 8:19 ` Steinar H. Gunderson
2022-03-16 11:19 ` Adrian Hunter
2022-03-16 12:59 ` Steinar H. Gunderson
2022-03-21 9:16 ` Adrian Hunter
2022-03-21 10:33 ` Steinar H. Gunderson [this message]
2022-03-21 13:09 ` Adrian Hunter
2022-03-21 16:58 ` Steinar H. Gunderson
2022-03-21 17:40 ` Adrian Hunter
2022-03-22 11:57 ` Steinar H. Gunderson
2022-03-29 12:31 ` Steinar H. Gunderson
2022-03-29 14:16 ` Steinar H. Gunderson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YjhUjotmo+kYvoNP@google.com \
--to=sesse@google.com \
--cc=acme@kernel.org \
--cc=adrian.hunter@intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).