Re: slow eMMC write speed

Praveen G K
2011-10-20T16:07:43Z

2011/10/20 Andrei Warkentin <awarkentin@vmware.com>:
> ----- Original Message -----
>> From: "Praveen G K" <praveen.gk@gmail.com>
>> To: "Andrei E. Warkentin" <andrey.warkentin@gmail.com>
>> Cc: "J Freyensee" <james_p_freyensee@linux.intel.com>, "Andrei Warkentin" <awarkentin@vmware.com>, "Per Förlin"
>> <per.forlin@stericsson.com>, "Linus Walleij" <linus.walleij@linaro.org>, linux-mmc@vger.kernel.org, "Arnd Bergmann"
>> <arnd@arndb.de>, "Jon Medhurst" <tixy@linaro.org>
>> Sent: Thursday, October 20, 2011 11:10:02 AM
>> Subject: Re: slow eMMC write speed
>>
>> 2011/10/20 Andrei E. Warkentin <andrey.warkentin@gmail.com>:
>> > 2011/10/19 Praveen G K <praveen.gk@gmail.com>:
>> >> Also, can somebody please tell me the significance of
>> >> blk_end_request? Thanks.
>> >> Why do we call this after every block read or write?
>> >
>> > Because you want to update the struct request with the amount
>> > written/read. If the entire
>> > requested I/O range has been satiffied, blk_end_request also calls
>> > blk_finish_request and
>> > completes the request.
>> Just for a quick understanding, I did the following
>>
>> During every eMMC write, I called the multi block write command with
>> the same set of data, and I called the mmc_end_request
>
> What's mmc_end_request? I'm assuming you meant blk_end_request.
Yes, you are right. I meant blk_end_request.

>> after  let's
>> say every 10 transfers (with each transfer being 128 blocks).  I
>> noticed that I did not see those big busy wait times as frequently as
>> compared to calling blk_end_request after every 128 block was
>> transferred.  Why is that happening?
>
> So you did 10 back-to-back 64k transfers inside the request handling routine, and you noticed that caused a smaller GC delay
> rather than doing 10 separate multiblock 64k transfers the normal way?
That's right. Even though the request is supposed to service only
64k, I sent 10 write commands each with 64k and then completed the
request (within the loop that takes care of the read/writes in
block.c) with the same data.

So, instead of calling blk_end_request just after one write, I call
blk_end_request after 10 writes.

> Depends. Maybe mmc_host_lazy_disable() (called by mmc_release_host) ends up doing some power management, which is bound
> to affect the card as well.
>
> Or maybe the card is trying to optimize consecutive writes into one larger write internally, and you're crossing some internal
> timestamp checking logic that distinguishes between separate and consecutive writes. You should talk to your manufacturer, and investigate what happens to your host on mmc_release_host.
>
> A
>