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 for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAPp3RGqifK=tum94nGKcqSmDpzj3ceC_ZDo7KNLOz4KHjqv5mw@mail.gmail.com>
Date:	Tue, 27 Aug 2013 12:01:01 -0500
From:	Robin Holt <robinmholt@...il.com>
To:	Alex Thorlton <athorlton@....com>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Dave Hansen <dave.hansen@...el.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Jones <davej@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 1/8] THP: Use real address for NUMA policy

Alex,

Although the explanation seems plausible, have you verified this is
actually possible?  You could make a simple pthread test case which
allocates a getpagesize() * <number-of-threads> area, prints its
address and then each thread migrate and reference their page.  Have
the task then sleep(<long-time>) before exit.  Look at the physical
address space with dlook for those virtual addresses in both the THP
and non-THP cases.

Thanks,
Robin

On Tue, Aug 27, 2013 at 11:50 AM, Alex Thorlton <athorlton@....com> wrote:
>> Here's more up-to-date version: https://lkml.org/lkml/2012/8/20/337
>
> These don't seem to give us a noticeable performance change either:
>
> With THP:
>
> real    22m34.279s
> user    10797m35.984s
> sys     39m18.188s
>
> Without THP:
>
> real    4m48.957s
> user    2118m23.208s
> sys     113m12.740s
>
> Looks like we got a few minutes faster on the with THP case, but it's
> still significantly slower, and that could just be a fluke result; we're
> still floating at about a 5x performance degradation.
>
> I talked with one of our performance/benchmarking experts last week and
> he's done a bit more research into the actual problem here, so I've got
> a bit more information:
>
> The real performance hit, based on our testing, seems to be coming from
> the increased latency that comes into play on large NUMA systems when a
> process has to go off-node to read from/write to memory.
>
> To give an extreme example, say we have a 16 node system with 8 cores
> per node. If we have a job that shares a 2MB data structure between 128
> threads, with THP on, the first thread to touch the structure will
> allocate all 2MB of space for that structure in a 2MB page, local to its
> socket.  This means that all the memory accessses for the other 120
> threads will be remote acceses.  With THP off, each thread could locally
> allocate a number of 4K pages sufficient to hold the chunk of the
> structure on which it needs to work, significantly reducing the number
> of remote accesses that each thread will need to perform.
>
> So, with that in mind, do we agree that a per-process tunable (or
> something similar) to control THP seems like a reasonable method to
> handle this issue?
>
> Just want to confirm that everyone likes this approach before moving
> forward with another revision of the patch.  I'm currently in favor of
> moving this to a per-mm tunable, since that seems to make more sense
> when it comes to threaded jobs. Also, a decent chunk of the code I've
> already written can be reused with this approach, and prctl will still
> be an appropriate place from which to control the behavior. Andrew
> Morton suggested possibly controlling this through the ELF header, but
> I'm going to lean towards the per-mm route unless anyone has a major
> objection to it.
>
> - Alex
--
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