Re: [PATCH v3] coccicheck: process every source file at once

From: Jeff King <peff@peff.net>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: Jacob Keller <jacob.keller@gmail.com>,
	Jacob Keller <jacob.e.keller@intel.com>,
	Git mailing list <git@vger.kernel.org>
Subject: Re: [PATCH v3] coccicheck: process every source file at once
Date: Wed, 10 Oct 2018 09:59:52 -0400	[thread overview]
Message-ID: <20181010135952.GA2933@sigill.intra.peff.net> (raw)
In-Reply-To: <20181010114441.GD23446@szeder.dev>

On Wed, Oct 10, 2018 at 01:44:41PM +0200, SZEDER Gábor wrote:

> > So that's really weird and counter-intuitive, since we should be doing
> > strictly less work. I know that spatch tries to parallelize itself,
> > though from my tests, 1.0.4 does not. I wonder if the version in Travis
> > differs in that respect and starts too many threads, and the extra time
> > is going to contention and context switches.
> 
> I don't think it does any parallel work.
> 
> Here is the timing again from my previous email:
> 
>   960.50user 22.59system 16:23.74elapsed 99%CPU (0avgtext+0avgdata 1606156maxresident)k
> 
> Notice that 16:23 is 983s, and that it matches the sum of the user and
> system times.  I usually saw this kind of timing with CPU-intensive
> single-threaded programs, and if there were any parallelization, then I
> would expect the elapsed time to be at least somewhat smaller than the
> other two.

Ah, right, I should have been able to figure that out myself. So scratch
that theory. My "hypervisor stalling our memory reads" theory is still
plausible, but I don't know how we would test it.

I guess in some sense it doesn't matter. If it's slower, we're not
likely to be able to fix that. So I guess we just need the fallback to
the current behavior.

-Peff