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

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Message-Id: <20150825202710.d960a928.akpm@linux-foundation.org>
Date:	Tue, 25 Aug 2015 20:27:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jason Low <jason.low2@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Terry Rudd <terry.rudd@...com>, Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 0/3] timer: Improve itimers scalability

On Tue, 25 Aug 2015 20:17:45 -0700 Jason Low <jason.low2@...com> wrote:

> When running a database workload on a 16 socket machine, there were
> scalability issues related to itimers.
> 
> Commit 1018016c706f addressed the issue with the thread_group_cputimer
> spinlock taking up a significant portion of total run time.
> 
> This patch series address the other issue where a lot of time is spent
> trying to acquire the sighand lock. It was found in some cases that
> 200+ threads were simultaneously contending for the same sighand lock,
> reducing throughput by more than 30%.

Does this imply that the patchset increased the throughput of this
workload by 30%?

And is this test case realistic?  If not, what are the benefits on a
real-world workload?

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