Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753094AbbDBPMX (ORCPT <rfc822;w@1wt.eu>);
	Thu, 2 Apr 2015 11:12:23 -0400
Received: from g4t3426.houston.hp.com ([15.201.208.54]:38478 "EHLO
	g4t3426.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751781AbbDBPMU convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 2 Apr 2015 11:12:20 -0400
From: "Elliott, Robert (Server Storage)" <Elliott@hp.com>
To: Christoph Hellwig <hch@lst.de>
CC: "linux-nvdimm@ml01.01.org" <linux-nvdimm@ml01.01.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        "boaz@plexistor.com" <boaz@plexistor.com>,
        "Kani, Toshimitsu" <toshi.kani@hp.com>
Subject: RE: another pmem variant V2
Thread-Topic: another pmem variant V2
Thread-Index: AQHQZ5+JacS38fCB50eh5aSIiWDyPZ03JjBggACkzgCAAg9A8A==
Date: Thu, 2 Apr 2015 15:11:36 +0000
Message-ID: <94D0CD8314A33A4D9D801C0FE68B40295A856737@G9W0745.americas.hpqcorp.net>
References: <1427358764-6126-1-git-send-email-hch@lst.de>
 <94D0CD8314A33A4D9D801C0FE68B40295A853392@G9W0745.americas.hpqcorp.net>
 <20150401072608.GA24312@lst.de>
In-Reply-To: <20150401072608.GA24312@lst.de>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
x-originating-ip: [16.210.48.26]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 3187
Lines: 90



> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@lst.de]
> Sent: Wednesday, April 1, 2015 2:26 AM
> To: Elliott, Robert (Server Storage)
> Cc: Christoph Hellwig; linux-nvdimm@ml01.01.org; linux-
> fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; x86@kernel.org;
> ross.zwisler@linux.intel.com; axboe@kernel.dk; boaz@plexistor.com; Kani,
> Toshimitsu
> Subject: Re: another pmem variant V2
> 
> On Tue, Mar 31, 2015 at 10:11:29PM +0000, Elliott, Robert (Server Storage)
> wrote:
> > I used fio to test 4 KiB random read and write IOPS
> > on a 2-socket x86 DDR4 system.  With various cache attributes:
> >
> > attr	read		write		notes
> > ----	----		-----		-----
> > UC	37 K		21 K		ioremap_nocache
> > WB	3.6 M		2.5 M		ioremap
> > WC	764 K		3.7 M		ioremap_wc
> > WT	<not tested yet>		ioremap_wt
> >
> > So, although UC and WT are the only modes certain to be safe,
> > the V1 default of UC provides abysmal performance - worse than
> > a consumer-class SATA SSD.
> 
> It doesn't look quite as bad on my setup, but performance is fairly
> bad here as well.
> 
> > A solution for x86 is to use the MOVNTI instruction in WB
> > mode. This non-temporal hint uses a buffer like the write
> > combining buffer, not filling the cache and not stopping
> > everything in the CPU.  The kernel function __copy_from_user()
> > uses that instruction (with SFENCE at the end) - see
> > arch/x86/lib/copy_user_nocache_64.S.
> >
> > If I made the change from memcpy() to __copy_from_user()
> > correctly, that results in:
> >
> > attr		read		write		notes
> > ----		----		-----		-----
> > WB w/NTI	2.4 M		2.6 M		__copy_from_user()
> > WC w/NTI	3.2 M		2.1 M		__copy_from_user()
> 
> That looks a lot better.  It doesn't help us with a pmem device
> mapped directly into userspace using mmap with the DAX infrastructure,
> though.
> 
> Note when we want to move to non-temporal copies we'll need to add
> a new prototype, as __copy_from_user isn't guaranteed to use these,
> and it is defined to only work on user addresses.  That doesn't matter
> on x86 but would blow up on say sparc or s390.

Here are some updated numbers including:
* WT (writethrough) cache attribute
* memcpy that uses non-temporal stores (MOVNTDQ) to the 
  persistent memory for block writes (rather than MOVNTI)
* memcpy that uses non-temporal loads (MOVNTDQA) from the 
  persistent memory for block reads

Attr	Copy		Read IOPS		Write IOPS
====	====		=========		==========
UC	memcpy		36 K			22 K
UC	NT rd,wr	513 K			326 K

WB	memcpy		3.4 M			2.5 M
WB	NT rd,wr	3.3 M			3.5 M

WC	memcpy		776 K			3.5 M
WC	NT rd,wr	3.0 M			3.9 M

WT	memcpy		2.1 M			22 K
WT	NT rd,wr	3.3 M			2.1 M

a few other variations yielded the peak numbers:
WC	NT rd only	3.2 M			4.1 M
WC	NT wr only	712 K			4.6 M
WT	NT wr only	2.6 M			4.0 M

There are lots of tuning considerations for those memcpy 
functions - how far to unroll the loop, whether to
include PRFETCHNTA instructions, etc.

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