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Date: Thu, 21 May 2009 16:11:17 -0700
Message-ID: <45e8e6c40905211611q256a71f1pb08e2014f7ed0775@mail.gmail.com>
Subject: Re: Throughput is not changed when setting to a much higher bit rate
From: Andrey Yurovsky <andrey@cozybit.com>
To: Dan Williams <dcbw@redhat.com>
Cc: Dongas <dongas86@gmail.com>,
	"John W. Linville" <linville@tuxdriver.com>,
	linux-wireless@vger.kernel.org
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On Thu, May 21, 2009 at 3:38 PM, Dan Williams <dcbw@redhat.com> wrote:
> On Thu, 2009-05-21 at 08:00 +0800, Dongas wrote:
>> 2009/5/21 Dan Williams <dcbw@redhat.com>:
>> > On Wed, 2009-05-20 at 22:48 +0800, Dongas wrote:
>> >> 2009/5/20 John W. Linville <linville@tuxdriver.com>:
>> >> > On Wed, May 20, 2009 at 01:48:32AM +0800, Dongas wrote:
>> >> >
>> >> >> Why the bandwidth is not changed when bit rate is changed to 11Mb/s?
>> >> >> Any thing wrong?
>> >> >
>> >> > More errors at higher bit rate, resulting in more retries? ?Just a
>> >> > thought...
>> >> >
>> >> Is there a quick way to verify this possible reason? I'm using Libertas driver.
>> >>
>> >> BTW, my sdio host driver is using polling mode to handle SDIO IRQ.
>> >> Could this be the cause of such poor performance?
>> >
>> > Definitely. ?With libertas, the largest class of issues by *far* that
>> > we've seen are controller related. ?I seem to recall that I've pulled
>> > about 6Mbps through the card using a normal Ricoh controller from a
>> > Fujitsu laptop. ?I can recheck that.
>>
>> AFAIK, most old laptop ,including my x61, doesn't support SDIO in HW.
>> So did Ricoh controller you tested use polling mode to handle SDIO IRQ?
>> Which clock of controller and which bit rate did you test?
>
> Actually, most of the older machines *can* do SDIO, those made from
> about 2006 - 2009. ?These days a lot of the SD "controllers" are
> actually USB-based mass-storage converters and cannot do SDIO, they are
> essentially 10-in-1 cardreaders.
>
> What is the 'lspci' output for your Thinkpad? ?If the controller isn't
> in 'lspci' but is in 'lsusb', then it's quite unlikely to work because
> of the above reason, I think.

Right, you need a real SDIO (vs. SD storage) controller on the PCI
bus.  However I can confirm that the ThinkPad X61 (and T61) controller
does full SDIO and you can plug Libertas SDIO cards into it.  The
older X-series ThinkPads (I tried the X40 and X41) work great too.

>> >> (However I just can't believe the performance is so poor ,only around
>> >> 1.1Mbps, with polling mode of SDIO IRQ)
>> >
>> > What specific kernel version are you using? ?There have been some
>> > latency fixes in recent kernels, but would be good to know just to make
>> > sure.
>>
>> I'm using kenrel 2.6.25.
>>
>> Thanks
>>
>> Regards
>> Dongas
>
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