Date: Thu, 27 Aug 2015 10:47:07 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Hideaki Kimura <hideaki.kimura@hpe.com>, Jason Low <jason.low2@hp.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH 0/3] timer: Improve itimers scalability
Message-ID: <20150827104707.6943c312@gandalf.local.home>
In-Reply-To: <20150827131844.GB21105@lerouge>
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	<1440626847.23728.122.camel@j-VirtualBox>
	<55DE4366.9080104@hpe.com>
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On Thu, 27 Aug 2015 15:18:49 +0200
Frederic Weisbecker <fweisbec@gmail.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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