linux-kernel - Re: [PATCHv2 0/9] split page table lock for PMD tables

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Date:	Thu, 19 Sep 2013 12:17:27 -0500
From:	Alex Thorlton <athorlton@....com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Dave Jones <davej@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Robin Holt <robinmholt@...il.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 0/9] split page table lock for PMD tables

On Mon, Sep 16, 2013 at 02:25:31PM +0300, Kirill A. Shutemov wrote:
> Alex Thorlton noticed that some massivly threaded workloads work poorly,
> if THP enabled. This patchset fixes this by introducing split page table
> lock for PMD tables. hugetlbfs is not covered yet.
> 
> This patchset is based on work by Naoya Horiguchi.
> 
> Changes:
>  v2:
>   - reuse CONFIG_SPLIT_PTLOCK_CPUS for PMD split lock;
>   - s/huge_pmd_lock/pmd_lock/g;
>   - assume pgtable_pmd_page_ctor() can fail;
>   - fix format line in task_mem() for VmPTE;
> 
> Benchmark (from Alex): ftp://shell.sgi.com/collect/appsx_test/pthread_test.tar.gz
> Run on 4 socket Westmere with 128 GiB of RAM.

Kirill,

I'm hitting some performance issues with these patches on our larger
machines (>=128 cores/256 threads).  I've managed to livelock larger
systems with one of our tests (I'll publish this one soon), and I'm
actually seeing a performance hit on some of the smaller ones.  I'm
currently collecting some results to show the problems I'm hitting,
and trying to research what's causing the livelock.  For now I just
wanted to let you know that I'm seeing some issues.  I'll be in touch
with more details.

Sorry for the delayed response, I wanted to be really sure that I was
seeing problems before I put up a red flag.

- Alex
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