linux-kernel - Re: another pmem variant V2

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Date:	Thu, 2 Apr 2015 18:41:39 +0200
From:	Christoph Hellwig <hch@....de>
To:	"Elliott, Robert (Server Storage)" <Elliott@...com>
Cc:	Christoph Hellwig <hch@....de>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	"boaz@...xistor.com" <boaz@...xistor.com>,
	"Kani, Toshimitsu" <toshi.kani@...com>
Subject: Re: another pmem variant V2

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?
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