Messages in this thread | | | Date | Wed, 3 Jun 2009 08:33:41 +0200 | From | Pierre Ossman <> | Subject | Re: Speed of SDHCI subsystem |
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On Tue, 19 May 2009 00:37:50 +0200 "J.A. Magallón" <jamagallon@ono.com> wrote:
> 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 ? >
Given your numbers I'd guess that your USB reader supports high-speed and your built-in one does not. The theoretical throughput without high-speed is 12.5 MB/s (SI-prefix). With some overhead, and the fact that many controllers have a lower maximum frequency than 25 MHz, makes your 10 MB/s pretty reasonable.
For reference, I've managed to achieve ~23 MB/s using a Sandisk Extreme III card and a JMicron controller, so there doesn't seem to be any major inherent bottle necks in the MMC stack.
Rgds -- -- Pierre Ossman
Linux kernel, MMC maintainer http://www.kernel.org rdesktop, core developer http://www.rdesktop.org TigerVNC, core developer http://www.tigervnc.org
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