lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20150610073512.GA17226@gmail.com>
Date:	Wed, 10 Jun 2015 09:35:12 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Waiman Long <Waiman.Long@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH v2 2/2] locking/qrwlock: Don't contend with readers when
 setting _QW_WAITING


* Waiman Long <Waiman.Long@...com> wrote:

> The current cmpxchg() loop in setting the _QW_WAITING flag for writers
> in queue_write_lock_slowpath() will contend with incoming readers
> causing possibly extra cmpxchg() operations that are wasteful. This
> patch changes the code to do a byte cmpxchg() to eliminate contention
> with new readers.
> 
> A multithreaded microbenchmark running 5M read_lock/write_lock loop
> on a 8-socket 80-core Westmere-EX machine running 4.0 based kernel
> with the qspinlock patch have the following execution times (in ms)
> with and without the patch:
> 
> With R:W ratio = 5:1
> 
> 	Threads	   w/o patch	with patch	% change
> 	-------	   ---------	----------	--------
> 	   2	     990 	    895		  -9.6%
> 	   3	    2136 	   1912		 -10.5%
> 	   4	    3166	   2830		 -10.6%
> 	   5	    3953	   3629		  -8.2%
> 	   6	    4628	   4405		  -4.8%
> 	   7	    5344	   5197		  -2.8%
> 	   8	    6065	   6004		  -1.0%
> 	   9	    6826	   6811		  -0.2%
> 	  10	    7599	   7599		   0.0%
> 	  15	    9757	   9766		  +0.1%
> 	  20	   13767	  13817		  +0.4%
> 
> With small number of contending threads, this patch can improve
> locking performance by up to 10%. With more contending threads,
> however, the gain diminishes.

Mind posting the microbenchmark?

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ