[RFC PATCH] disk: Don't loop over MAX_SEARCH_PARTITIONS in part_create_block_devices()

[Stefan Roese]

On 1/11/23 02:32, AKASHI Takahiro wrote:
> Hi,
> 
> Thank you for catching this issue.
> 
> On Tue, Jan 10, 2023 at 09:00:38AM +0100, Stefan Roese wrote:
>> I've noticed that the first ext4 file loading from a MMC partition for
>> ZynqMP takes quite some time (~ 1 second). Debugging showed, that the
>> MMC driver reads the partition info 128 time (MAX_SEARCH_PARTITIONS)
>> resulting in this boot delay. To fix this, let's just end creating the
>> block drives in part_create_block_devices() when no more valid partition
>> is found. This reduces the first file reading from ~0.9s to ~0.3s.
>>
>> Signed-off-by: Stefan Roese <sr at denx.de>
>> Cc: Simon Glass <sjg at chromium.org>
>> Cc: AKASHI Takahiro <takahiro.akashi at linaro.org>
>> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> ---
>> Reasoning for RFC:
>> I did not dig into the current disk / partition stuff too deeply, so I'm
>> not 100% sure that this patch does not break anything.
> 
> I'm afraid that this fix won't work for all the partition types,
> especially for those in which entries in a partition table can be sparsely filled,
> or in other words, valid partition numbers may not always be contiguous
> even if they don't reach a maximum number.

So what is the maximum number? Where originates the
MAX_SEARCH_PARTITIONS = 128 from?

> I somehow confirmed this against a GPT partition by using gdisk.

How exactly did you confirm this?

Thanks,
Stefan

> -Takahiro Akashi
> 
>> ---
>>   disk/disk-uclass.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/disk/disk-uclass.c b/disk/disk-uclass.c
>> index d32747e2242d..2999f7285b5a 100644
>> --- a/disk/disk-uclass.c
>> +++ b/disk/disk-uclass.c
>> @@ -36,7 +36,7 @@ int part_create_block_devices(struct udevice *blk_dev)
>>   	/* Add devices for each partition */
>>   	for (count = 0, part = 1; part <= MAX_SEARCH_PARTITIONS; part++) {
>>   		if (part_get_info(desc, part, &info))
>> -			continue;
>> +			break;
>>   		snprintf(devname, sizeof(devname), "%s:%d", blk_dev->name,
>>   			 part);
>>   
>> -- 
>> 2.39.0
>>

Viele Grüße,
Stefan Roese

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