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Date: Thu, 2 Apr 2015 18:41:39 +0200
From: Christoph Hellwig <hch@lst.de>
To: "Elliott, Robert (Server Storage)" <Elliott@hp.com>
Cc: Christoph Hellwig <hch@lst.de>,
        "linux-nvdimm@ml01.01.org" <linux-nvdimm@ml01.01.org>,
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        "boaz@plexistor.com" <boaz@plexistor.com>,
        "Kani, Toshimitsu" <toshi.kani@hp.com>
Subject: Re: another pmem variant V2
Message-ID: <20150402164139.GA9774@lst.de>
References: <1427358764-6126-1-git-send-email-hch@lst.de> <94D0CD8314A33A4D9D801C0FE68B40295A853392@G9W0745.americas.hpqcorp.net> <20150401072608.GA24312@lst.de> <94D0CD8314A33A4D9D801C0FE68B40295A856737@G9W0745.americas.hpqcorp.net>
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On Thu, Apr 02, 2015 at 03:11:36PM +0000, Elliott, Robert (Server Storage) wrote:
> 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.

Looks like we should aіm for WC + NT would be a good start.

Can you prepare a patch to add your NT memcpy variants and
a second one to use them in the pmem driver?