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Date: Thu, 28 Oct 2021 22:01:34 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Kalesh Singh <kaleshsingh@...gle.com> Cc: surenb@...gle.com, hridya@...gle.com, namhyung@...nel.org, kernel-team@...roid.com, mhiramat@...nel.org, zanussi@...nel.org, Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] tracing/histogram: Optimize division by constants On Wed, 27 Oct 2021 20:28:54 -0700 Kalesh Singh <kaleshsingh@...gle.com> wrote: > +/* > + * Returns the specific division function to use if the divisor > + * is constant. This avoids extra branches when the trigger is hit. > + */ > +static hist_field_fn_t hist_field_get_div_fn(struct hist_field *divisor) > +{ > + u64 div; > + > + if (divisor->flags & HIST_FIELD_FL_VAR_REF) { > + struct hist_field *var; > + > + var = find_var_field(divisor->var.hist_data, divisor->name); > + div = var->constant; > + } else > + div = divisor->constant; > + > + if (!div) > + return div_by_zero; Do we really need a div_by_zero constant function? What about just erroring here and perhaps return -EDOM? -- Steve > + > + if (!(div & (div - 1))) > + return div_by_power_of_two; > + > + /* If the divisor is too large, do a regular division */ > + if (div > (1 << HIST_DIV_SHIFT)) > + return div_by_not_power_of_two; > + > + divisor->div_multiplier = div64_u64((u64)(1 << HIST_DIV_SHIFT), div); > + return div_by_mult_and_shift; > +} > +
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