linux-kernel - Re: [RFC PATCH RT] rwsem: The return of multi-reader PI rwsems

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Message-ID: <5346B2C8.6000207@linutronix.de>
Date:	Thu, 10 Apr 2014 17:03:36 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Clark Williams <williams@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH RT] rwsem: The return of multi-reader PI rwsems

On 04/10/2014 04:44 PM, Clark Williams wrote:
> The means of each group of five test runs are:
> 
> vanilla.log:  1210117 rt.log:  17210953 (14.2 x slower than
> vanilla) rt-fixes.log:  10062027 (8.3 x slower than vanilla) 
> rt-multi.log:  3179582  (2.x x slower than vanilla)
> 
> 
> As expected, vanilla kicked RT's butt when hammering on the 
> mmap_sem. But somewhat unexpectedly, your fixups helped quite a
> bit and the multi+fixups got RT back into being almost
> respectable.
> 
> Obviously these are just preliminary results on one piece of h/w
> but it looks promising.

Is it easy to look at the latency when you have multiple readers and
and a high prio writer which has to boost all those readers away
instead just one?
Or is this something that should not happen for a high prio RT task
because it has all memory already allocated?

> 
> Clark

Sebastian
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