linux-kernel - Re: [PATCH v2 1/4] tracing/histogram: Optimize division by constants

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Message-ID: <CAC_TJvfazjdZ=4Y_1YX=R+drsWKRu+faztcFjKEkkD_3Qk6_Xg@mail.gmail.com>
Date:   Fri, 29 Oct 2021 15:31:40 -0700
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     surenb@...gle.com, hridya@...gle.com, namhyung@...nel.org,
        kernel-team@...roid.com, mhiramat@...nel.org,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/4] tracing/histogram: Optimize division by constants

On Fri, Oct 29, 2021 at 1:25 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Fri, 29 Oct 2021 11:53:16 -0700
> Kalesh Singh <kaleshsingh@...gle.com> wrote:
>
> > > If these functions are only called when val2 is constant, can't we make it
> > > such that we get val2 from the hist_field directly? That is:
> > >
> > >         u64 val2 = operand2->constant;
> >
> > operand2 might be a var ref to a constant, so we would need to resolve
> > that with hist_field_var_ref().
>
> So can a var_ref change? If not, then we should convert that to a constant
> for this operation.

A var ref to a constant won't change. I think we can just copy the
constant value to the var ref's hist field and then we'll be able to
get it from there instead of calling the fn() function. I'll post
another version with this.

Thanks,
Kalesh

>
> -- Steve