linux-kernel - Re: [PATCH 0/3] timer: Improve itimers scalability

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Message-ID: <20150827104707.6943c312@gandalf.local.home>
Date:	Thu, 27 Aug 2015 10:47:07 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Hideaki Kimura <hideaki.kimura@....com>,
	Jason Low <jason.low2@...com>, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 0/3] timer: Improve itimers scalability

On Thu, 27 Aug 2015 15:18:49 +0200
Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Wed, Aug 26, 2015 at 04:45:44PM -0700, Hideaki Kimura wrote:
> > I totally agree that this is not a perfect solution. If there are 10x more
> > cores and sockets, just the atomic fetch_add might be too expensive.
> > 
> > However, it's comparatively/realistically the best thing we can do without
> > any drawbacks. We can't magically force all library developers to write the
> > most scalable code always.
> > 
> > My point is: this is a safety net, and a very effective one.
> 
> I mean the problem here is that a library uses an unscalable profiling feature,
> unconditionally as soon as you load it without even initializing anything. And
> this library is used in production.
> 
> At first sight, fixing that in the kernel is only a hack that just reduces a bit
> the symptoms.
> 
> What is the technical issue that prevents from fixing that in the library itself?
> Posix timers can be attached anytime.

I'm curious to what the downside of this patch set is? If we can fix a
problem that should be fixed in userspace, but does not harm the kernel
by doing so, is that bad? (an argument for kdbus? ;-)


As Hideaki noted, this could be a problem in other locations as well
that people have yet to find.

-- Steve
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