Re: [PATCH 0/2] /proc/stat: Reduce irqs counting performance overhead

From: Daniel Colascione
Date: Mon Jan 07 2019 - 17:41:42 EST

On Mon, Jan 7, 2019 at 5:32 PM Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Mon, Jan 07, 2019 at 10:12:56AM -0500, Waiman Long wrote:
> > As newer systems have more and more IRQs and CPUs available in their
> > system, the performance of reading /proc/stat frequently is getting
> > worse and worse.
> Because the "roll-your-own" per-cpu counter implementaiton has been
> optimised for low possible addition overhead on the premise that
> summing the counters is rare and isn't a performance issue. This
> patchset is a direct indication that this "summing is rare and can
> be slow" premise is now invalid.

Focusing on counter performance is, IMHO, missing the mark. Even if
interrupt count collection were made fast, there's *something* in any
particular /proc file that a particular reader doesn't need and that,
by being uselessly collected, needlessly slows that reader. There
should be a general-purpose way for /proc file readers to tell the
kernel which bits of information interest them on a particular read
syscall sequence or particular open(2) or something. Creating a new
proc file for every useful combination of attributes doesn't scale