linux-kernel - Re: [PATCH] procfs: export context switch counts in /proc/*/stat

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Date:	Wed, 20 Dec 2006 12:36:23 -0500
From:	"Albert Cahalan" <acahalan@...il.com>
To:	"David Wragg" <david@...gg.org>
Cc:	linux-kernel@...r.kernel.org, bcrl@...ck.org
Subject: Re: [PATCH] procfs: export context switch counts in /proc/*/stat

On 12/20/06, David Wragg <david@...gg.org> wrote:
> "Albert Cahalan" <acahalan@...il.com> writes:
> > On Mon, Dec 18, 2006 at 11:50:08PM +0000, David Wragg wrote:
> >> This patch (against 2.6.19/2.6.19.1) adds the four context
> >> switch values (voluntary context switches, involuntary
> >> context switches, and the same values accumulated from
> >> terminated child processes) to the end of /proc/*/stat,
> >> similarly to min_flt, maj_flt and the time used values.
> >
> > Hmmm, OK, do people have a use for these values?
>
> My reason for writing the patch was to track which processes are
> active (i.e. got scheduled to run) by polling these context switch
> values.  The time used values are not a reliable way to detect process
> activity on fast machines.  So for example, when sorting by %CPU, top
> often shows many processes using 0% CPU, despite the fact that these
> processes are running occasionally.  If top sorted by (%CPU, context
> switch count delta), it might give a more useful display of which
> processes are active on the system.

Oh, that'd be great.

The cumulative ones are still not justified though, and I fear they
may be 64-bit even on i386. It turns out that an i386 procps spends
much of its time doing 64-bit division to parse the damn ASCII crap.
I suppose I could just skip those fields, but generating them isn't
too cheap and probably I'd get stuck parsing them for some other
reason -- having them separate is probably a good idea.
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