linux-kernel - [PATCH v2 0/4] timer: Improve itimers scalability

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Date:	Wed, 14 Oct 2015 12:07:52 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	George Spelvin <linux@...izon.com>, hideaki.kimura@....com,
	terry.rudd@....com, scott.norton@....com,
	Jason Low <jason.low2@...com>
Subject: [PATCH v2 0/4] timer: Improve itimers scalability

While running a database workload on a 16 socket machine, there were
scalability issues related to itimers. The following link contains a
more detailed summary of the issues at the application level.

https://lkml.org/lkml/2015/8/26/737

Commit 1018016c706f addressed the issue with the thread_group_cputimer
spinlock taking up a significant portion of total run time.
This patch series addresses the secondary 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%.

With this patch set (along with commit 1018016c706f mentioned above),
the performance hit of itimers almost completely goes away on the
16 socket system.

Jason Low (4):
  timer: Optimize fastpath_timer_check()
  timer: Check thread timers only when there are active thread timers
  timer: Convert cputimer->running to bool
  timer: Reduce unnecessary sighand lock contention

 include/linux/init_task.h      |    3 +-
 include/linux/sched.h          |    9 ++++--
 kernel/fork.c                  |    2 +-
 kernel/time/posix-cpu-timers.c |   63 ++++++++++++++++++++++++++++-----------
 4 files changed, 54 insertions(+), 23 deletions(-)

-- 
1.7.2.5

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