linux-kernel - Re: [PATCH v2 2/5] tracing: Add division and multiplication support for hist triggers

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Message-ID: <20211020111301.0032a43d@gandalf.local.home>
Date:   Wed, 20 Oct 2021 11:13:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] tracing: Add division and multiplication support
 for hist triggers

On Wed, 20 Oct 2021 07:54:59 -0700
Kalesh Singh <kaleshsingh@...gle.com> wrote:

> Is it worth adding something like this for the multiplication case as well?

No, multiplication is a pretty fast operation, and the added branches to
test would cause more overhead than what you would save. But, division is a
very slow operation, and I believe that even with the extra branches it
would still help.

If we do this, it should be a separate patch anyway, where we can actual do
measurements to see if there was an improvement, and revert if not.

-- Steve