[PATCH v3 1/3] mmc: dw_mmc: fix the max_blk_count in IDMAC

[Sonny Rao]

On Sat, Jan 3, 2015 at 4:51 PM, Alim Akhtar <alim.akhtar at gmail.com> wrote:
> Hi Doug / Sonny
> New year greetings!!
>
> On Sat, Jan 3, 2015 at 4:37 AM, Doug Anderson <dianders at chromium.org> wrote:
>> Alim,
>>
>> On Mon, Dec 22, 2014 at 4:12 AM, Alim Akhtar <alim.akhtar at samsung.com> wrote:
>>> From: Seungwon Jeon <tgih.jun at samsung.com>
>>>
>>> Even though 1MB is reserved for descriptor table in IDMAC,
>>> the dw_mmc host driver is allowed to receive only maximum
>>> 128KB block length in one request. This is caused by setting
>>> improper max_blk_count. It needs to be e adjusted so that
>>> descriptor table is used fully. It is found that the performance
>>> is improved with the increased the max_blk_count.
>>>
>>> Signed-off-by: Seungwon Jeon <tgih.jun at samsung.com>
>>> Acked-by: Jaehoon Chung <jh80.chung at samsung.com>
>>> Signed-off-by: Alim Akhtar <alim.akhtar at samsung.com>
>>> ---
>>>  drivers/mmc/host/dw_mmc.c |    4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>> index 64ea042..a1b80e5 100644
>>> --- a/drivers/mmc/host/dw_mmc.c
>>> +++ b/drivers/mmc/host/dw_mmc.c
>>> @@ -2332,9 +2332,9 @@ static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
>>>  #ifdef CONFIG_MMC_DW_IDMAC
>>>                 mmc->max_segs = host->ring_size;
>>>                 mmc->max_blk_size = 65536;
>>> -               mmc->max_blk_count = host->ring_size;
>>>                 mmc->max_seg_size = 0x1000;
>>> -               mmc->max_req_size = mmc->max_seg_size * mmc->max_blk_count;
>>> +               mmc->max_req_size = mmc->max_seg_size * host->ring_size;
>>> +               mmc->max_blk_count = mmc->max_req_size / 512;
>>
>> The numbers are a little different than the ones you and Sonny arrived
>> at about a year ago at
>> <https://chromium-review.googlesource.com/#/c/176488/>
>>
>> You end up with the same max_req_size I think, but it looks as if
>> max_blk_count is 0x800 in your series and ix 0xffff in the one from a
>> year ago.  Do you have any explanation for why it is max_req_size /
>> 512?
>>
> Before taking this patch, I went over all the discussions that had
> happened in past
> http://marc.info/?l=linux-mmc&m=133039478518090&w=2 (way back in 2012)
> http://www.spinics.net/lists/linux-mmc/msg25549.html
> and
> http://www.spinics.net/lists/linux-mmc/msg25797.html
>
> and the last one was having an ACK from maintainer.
>
> Having said that, I did check the performance number with current
> patch which has landed and with one which sets max_blk_count as
> 0xFFFF.
> And both given exactly the same numbers on peach-pi (Write: ~52MB/s
> and Read: ~146MB/s (HS200) using iozone),
>
> I checked it a bit more and found that in both the case
> max_hw_sectors_kb is set to 1024 (max request size to block layer) and
> max_hw_sectors_kb is the one which actually affect the Performance
> numbers and max_hw_sectors_kb is set as
>
> blk_queue_max_hw_sectors(mq->queue, min(host->max_blk_count,
> host->max_req_size / 512));
>
> In case of 64bit IDMAC (one on exynos7) which given a different value
> for "ring_size", both the patches set the same max_hw_sectors_kb (512
> in this case)
>
> Do you see some performance degradation with some other variants of
> dw_mmc host controller with current ToT?

Looks like Doug test it and saw a performance improvement on rk3288
Thanks!

>
> Sonny,
> I ran iozone like: iozone -az -i0 -i1 -I -s 10M -f /home/test (on eMMC)
>
>> -Doug
>
>
>
> --
> Regards,
> Alim