linux-kernel - Speed of SDHCI subsystem

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Message-ID: <20090519003750.461abe7d@werewolf.home>
Date:	Tue, 19 May 2009 00:37:50 +0200
From:	"J.A. Magallón" <jamagallon@....com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: Speed of SDHCI subsystem

Hi all...

I have notice something strange with SD cards.
I have an Aspire One and had an 8Gb SDHC card that used for my home,
and have recently upgraded to a 16Gb one.
This new one came with an USB reader.

The thing is that cards look much faster when accessed through the USB
key that directly on the readers of the One.

Some numbers with hdparm:

TakeMS 8Gb Class 6:
	Gives 10MB/s on the slot, 17MB/s via the USB key
SanDisk UltraII 16Gb, Class 4, advertised as 15Mb/s:
	Gives 10MB/s on the slot, 14MB/s on USB

I know that hdparm is not a benchmark, but I supposed it should be
limited by the media, not the connection.

But somehow the SDHCI/MMC subsystem seems to be stuck at 10MB/s, independent
of the quality of the media.

Any ideas ?

-- 
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2010.0 (Cooker) for x86_64
Linux 2.6.29.2-desktop-1mnb (gcc 4.3.2 (GCC) #1 Wed May
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