[U-Boot] [PATCH 1/2] common: usb_storage : Implement logic to calculate optimal usb maximum trasfer blocks

[Marek Vasut <marex@denx.de>]

On 05/31/2016 05:23 AM, Rajesh Bhagat wrote:
> 
> 
>> -----Original Message-----
>> From: Marek Vasut [mailto:marex at denx.de]
>> Sent: Tuesday, May 31, 2016 5:12 AM
>> To: Rajesh Bhagat <rajesh.bhagat@nxp.com>; u-boot at lists.denx.de
>> Cc: sjg at chromium.org; york sun <york.sun@nxp.com>; Sriram Dash
>> <sriram.dash@nxp.com>
>> Subject: Re: [PATCH 1/2] common: usb_storage : Implement logic to calculate
>> optimal usb maximum trasfer blocks
>>
>> On 05/30/2016 01:23 PM, Rajesh Bhagat wrote:
>>> Implements the logic to calculate the optimal usb maximum trasfer
>>> blocks instead of sending USB_MAX_XFER_BLK blocks which is 65535 and
>>> 20 in case of EHCI and other USB protocols respectively.
>>>
>>> It adds an array of trasfer blocks that should be checked for success
>>> starting from minimum to maximum, and rest of the read/write are
>>> performed with that optimal value. It tries to increase/decrease the
>>> blocks in follwing scenarios:
>>>
>>> 1.decrease blocks: when read/write for a particular number of blocks
>>> fails.
>>> 2. increase blocks: when read/write for a particular number of blocks
>>> pass and amount left to trasfer is greater than current number of
>>> blocks.
>>>
>>> Currently changes are done for EHCI where min = 4096 andmax = 65535 is
>>> taken. And for other cases code is left unchanged by keeping min = max
>>> = 20.
>>>
>>> Signed-off-by: Sriram Dash <sriram.dash@nxp.com>
>>> Signed-off-by: Rajesh Bhagat <rajesh.bhagat@nxp.com>
>>> ---
>>>  common/usb_storage.c |   54
>> ++++++++++++++++++++++++++++++++++++++++----------
>>>  1 file changed, 43 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/common/usb_storage.c b/common/usb_storage.c index
>>> 7e6e52d..7b5ad07 100644
>>> --- a/common/usb_storage.c
>>> +++ b/common/usb_storage.c
>>> @@ -101,16 +101,15 @@ struct us_data {  };
>>>
>>>  #ifdef CONFIG_USB_EHCI
>>> -/*
>>> - * The U-Boot EHCI driver can handle any transfer length as long as
>>> there is
>>> - * enough free heap space left, but the SCSI READ(10) and WRITE(10)
>>> commands are
>>> - * limited to 65535 blocks.
>>> - */
>>> -#define USB_MAX_XFER_BLK	65535
>>> +#define USB_XFER_BLK_TBL_SZ		5
>>> +static unsigned short usb_xfer_blk_tbl[5] = {4096, 8192, 16384,
>>> +32768, 65535};
>>
>> You should stick to using one block less than the power of two, the controllers react to
>> that a bit better. 
> 
> Hello Marek,
> 
> I agree to above point, Will change the logic to use one block less than power of two
> i.e. 4095, 8191... 65535
> 
>> Each value in this table can then be calculated really trivially, it's:
>>
>> (1 << (12 + n)) - 1
>>
> 
> Prior to current implementation, I created USB_MIN_XFER_BLK=4096 and 
> USB_MAX_XFER_BLK=65535 macros. And started the logic to multiple and divide 
> by two to reach USB_MAX_XFER_BLK. Then thought, calculation would be costlier 
> than indexing an array. 

Since the numbers are 16bit tops, they will most likely end up being
optimized to mov rN, #imm16 or mov rN, imm16 + sub rN, #1 . That's two
local instructions tops, which will always be at least as fast as any
memory fetch.

> Please comment. 
> 
>> You also don't need such static data.
>>
> 
> Let me share the background for keeping this variable, It is taken to store the 
> last optimal value for next read/write operation. And these value is reset to minimum
> when another USB device is connected.

Consider the scenario where you have two sticks plugged in and mix
reading from both. Your approach with static variable will fail miserably.

> Refer below log: 
> 
> 1st time (Iterated over all the possible size)
> => mw 81000000 55555555 4000000; mw a0000000 aaaaaaaa 4000000; usb write a0000000 0 80000; usb read 81000000 0 80000; cmp.b a0000000 81000000 10000000;
> 
> USB write: device 0 block # 0, count 524288 ... usb_read: retry #2, xfer_blk 4096, smallblks 4096
> usb_read: retry #2, xfer_blk 8192, smallblks 8192
> usb_read: retry #2, xfer_blk 16384, smallblks 16384
> usb_read: retry #2, xfer_blk 32768, smallblks 32768
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 4103
> 524288 blocks write: OK
> 
> 2nd time (It started form 65535 blocks as it is last optimal value)
> => mw 81000000 55555555 4000000; mw a0000000 aaaaaaaa 4000000; usb write a0000000 0 80000; usb read 81000000 0 80000; cmp.b a0000000 81000000 10000000;
> 
> USB write: device 0 block # 0, count 524288 ... usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 65535
> usb_read: retry #2, xfer_blk 65535, smallblks 8
> 524288 blocks write: OK
> 
> And I observed this value is different for read/write, Hence second patch is sent for handle 
> that situation. 
> 
> Best Regards,
> Rajesh Bhagat 
> 
>>>  #else
>>> -#define USB_MAX_XFER_BLK	20
>>> +#define USB_XFER_BLK_TBL_SZ		1
>>> +static unsigned short usb_xfer_blk_tbl[1] = {20};
>>>  #endif
>>>
>>> +static unsigned short USB_MAX_XFER_BLK;
>>
>> This value is different on per-device basis, how can it be static data ?
>>
>>>  #ifndef CONFIG_BLK
>>>  static struct us_data usb_stor[USB_MAX_STOR_DEV];  #endif @@ -1117,7
>>> +1116,8 @@ static unsigned long usb_stor_read(struct blk_desc *block_dev,
>> lbaint_t blknr,
>>>  	unsigned short smallblks;
>>>  	struct usb_device *udev;
>>>  	struct us_data *ss;
>>> -	int retry;
>>> +	int retry, next = LOG2((USB_MAX_XFER_BLK + 1) / usb_xfer_blk_tbl[0]);
>>> +	bool retry_flag = false;
>>>  	ccb *srb = &usb_ccb;
>>>  #ifdef CONFIG_BLK
>>>  	struct blk_desc *block_dev;
>>> @@ -1158,6 +1158,8 @@ static unsigned long usb_stor_read(struct blk_desc
>> *block_dev, lbaint_t blknr,
>>>  		else
>>>  			smallblks = (unsigned short) blks;
>>>  retry_it:
>>> +		debug("usb_read: retry #%d, xfer_blk %hu, smallblks %hu\n",
>>> +		      retry, USB_MAX_XFER_BLK, smallblks);
>>>  		if (smallblks == USB_MAX_XFER_BLK)
>>>  			usb_show_progress();
>>>  		srb->datalen = block_dev->blksz * smallblks; @@ -1165,14 +1167,26
>>> @@ retry_it:
>>>  		if (usb_read_10(srb, ss, start, smallblks)) {
>>>  			debug("Read ERROR\n");
>>>  			usb_request_sense(srb, ss);
>>> -			if (retry--)
>>> +			if (retry--) {
>>> +				/* decrease the USB_MAX_XFER_BLK */
>>> +				if (next >  0) {
>>> +					smallblks = usb_xfer_blk_tbl[--next];
>>> +					USB_MAX_XFER_BLK = smallblks;
>>> +				}
>>> +				retry_flag = true;
>>>  				goto retry_it;
>>> +			}
>>>  			blkcnt -= blks;
>>>  			break;
>>>  		}
>>>  		start += smallblks;
>>>  		blks -= smallblks;
>>>  		buf_addr += srb->datalen;
>>> +
>>> +		/* try to increase the USB_MAX_XFER_BLK */
>>> +		if (next < USB_XFER_BLK_TBL_SZ  - 1)
>>> +			if (!retry_flag && usb_xfer_blk_tbl[next + 1] <= blks)
>>> +				USB_MAX_XFER_BLK = usb_xfer_blk_tbl[++next];
>>>  	} while (blks != 0);
>>>  	ss->flags &= ~USB_READY;
>>>
>>> @@ -1199,7 +1213,8 @@ static unsigned long usb_stor_write(struct blk_desc
>> *block_dev, lbaint_t blknr,
>>>  	unsigned short smallblks;
>>>  	struct usb_device *udev;
>>>  	struct us_data *ss;
>>> -	int retry;
>>> +	int retry, next = LOG2((USB_MAX_XFER_BLK + 1) / usb_xfer_blk_tbl[0]);
>>> +	bool retry_flag = false;
>>>  	ccb *srb = &usb_ccb;
>>>  #ifdef CONFIG_BLK
>>>  	struct blk_desc *block_dev;
>>> @@ -1244,6 +1259,8 @@ static unsigned long usb_stor_write(struct blk_desc
>> *block_dev, lbaint_t blknr,
>>>  		else
>>>  			smallblks = (unsigned short) blks;
>>>  retry_it:
>>> +		debug("usb_write: retry #%d, xfer_blk %hu, smallblks %hu\n",
>>> +		      retry, USB_MAX_XFER_BLK, smallblks);
>>>  		if (smallblks == USB_MAX_XFER_BLK)
>>>  			usb_show_progress();
>>>  		srb->datalen = block_dev->blksz * smallblks; @@ -1251,14 +1268,26
>>> @@ retry_it:
>>>  		if (usb_write_10(srb, ss, start, smallblks)) {
>>>  			debug("Write ERROR\n");
>>>  			usb_request_sense(srb, ss);
>>> -			if (retry--)
>>> +			if (retry--) {
>>> +				/* decrease the USB_MAX_XFER_BLK */
>>> +				if (next >  0) {
>>> +					smallblks = usb_xfer_blk_tbl[--next];
>>> +					USB_MAX_XFER_BLK = smallblks;
>>> +				}
>>> +				retry_flag = true;
>>>  				goto retry_it;
>>> +			}
>>>  			blkcnt -= blks;
>>>  			break;
>>>  		}
>>>  		start += smallblks;
>>>  		blks -= smallblks;
>>>  		buf_addr += srb->datalen;
>>> +
>>> +		/* try to increase the USB_MAX_XFER_BLK */
>>> +		if (next < USB_XFER_BLK_TBL_SZ  - 1)
>>> +			if (!retry_flag && usb_xfer_blk_tbl[next + 1] <= blks)
>>> +				USB_MAX_XFER_BLK = usb_xfer_blk_tbl[++next];
>>>  	} while (blks != 0);
>>>  	ss->flags &= ~USB_READY;
>>>
>>> @@ -1331,6 +1360,9 @@ int usb_storage_probe(struct usb_device *dev, unsigned
>> int ifnum,
>>>  		break;
>>>  	}
>>>
>>> +	/* Initialize the current transfer blocks to minimum value */
>>> +	USB_MAX_XFER_BLK = usb_xfer_blk_tbl[0];
>>> +
>>>  	/*
>>>  	 * We are expecting a minimum of 2 endpoints - in and out (bulk).
>>>  	 * An optional interrupt is OK (necessary for CBI protocol).
>>>
>>
>>
>> --
>> Best regards,
>> Marek Vasut


-- 
Best regards,
Marek Vasut