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

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Message-ID: <20150827131844.GB21105@lerouge>
Date:	Thu, 27 Aug 2015 15:18:49 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Hideaki Kimura <hideaki.kimura@....com>
Cc:	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>,
	Steven Rostedt <rostedt@...dmis.org>,
	Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 0/3] timer: Improve itimers scalability

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.

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