From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Subject: Re: [PATCH 1/5] [PATCH 1/5] function-graph/x86: replace unbalanced ret with jmp
Date: Tue, 13 Oct 2009 23:02:10 +0200 [thread overview]
Message-ID: <20091013210208.GB5135@nowhere> (raw)
In-Reply-To: <20091013203425.042034383@goodmis.org>
On Tue, Oct 13, 2009 at 04:33:50PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> The function graph tracer replaces the return address with a hook to
> trace the exit of the function call. This hook will finish by returning
> to the real location the function should return to.
>
> But the current implementation uses a ret to jump to the real return
> location. This causes a imbalance between calls and ret. That is
> the original function does a call, the ret goes to the handler
> and then the handler does a ret without a matching call.
>
> Although the function graph tracer itself still breaks the branch
> predictor by replacing the original ret, by using a second ret and
> causing an imbalance, it breaks the predictor even more.
I have troubles to understand by it breaks the predictor, especially
since there is not conditional branch in return_to_handler.
But still I don't understand why a ret would break more the branch
prediction than a jmp.
next prev parent reply other threads:[~2009-10-13 21:03 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-13 20:33 [PATCH 0/5] [GIT PULL][2.6.33] tracing: various updates Steven Rostedt
2009-10-13 20:33 ` [PATCH 1/5] [PATCH 1/5] function-graph/x86: replace unbalanced ret with jmp Steven Rostedt
2009-10-13 20:47 ` Mathieu Desnoyers
2009-10-13 21:10 ` Steven Rostedt
2009-10-13 21:21 ` Mathieu Desnoyers
2009-10-13 21:26 ` Steven Rostedt
2009-10-13 22:32 ` Mathieu Desnoyers
2009-10-13 21:02 ` Frederic Weisbecker [this message]
2009-10-13 21:12 ` Steven Rostedt
2009-10-13 22:26 ` Frederic Weisbecker
2009-10-14 6:58 ` [tip:tracing/core] function-graph/x86: Replace " tip-bot for Steven Rostedt
2009-10-13 20:33 ` [PATCH 2/5] [PATCH 2/5] tracing: export symbols for kernel lock tracepoints Steven Rostedt
2009-10-13 20:43 ` Frederic Weisbecker
2009-10-13 21:14 ` Steven Rostedt
2009-10-13 20:33 ` [PATCH 3/5] [PATCH 3/5] tracing: support multiple pids in set_pid_ftrace file Steven Rostedt
2009-10-14 6:58 ` [tip:tracing/core] tracing: Support " tip-bot for jolsa@redhat.com
2009-10-13 20:33 ` [PATCH 4/5] [PATCH 4/5] tracing: enable records during the module load Steven Rostedt
2009-10-14 6:59 ` [tip:tracing/core] tracing: Enable " tip-bot for Jiri Olsa
2009-10-13 20:33 ` [PATCH 5/5] [PATCH 5/5] tracing: enabling "__cold" functions Steven Rostedt
2009-10-14 6:59 ` [tip:tracing/core] tracing: Enable " tip-bot for Jiri Olsa
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=20091013210208.GB5135@nowhere \
--to=fweisbec@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@polymtl.ca \
--cc=mingo@elte.hu \
--cc=rostedt@goodmis.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.