Re: [PATCH v3 01/11] md/raid5: add CONFIG_MD_RAID456_STRIPE_SHIFT to set STRIPE_SIZE

[Yufen Yu <yuyufen@huawei.com>]

On 2020/5/27 21:54, Guoqing Jiang wrote:
> Hi,
> 
> On 5/27/20 3:19 PM, Yufen Yu wrote:
>>   +config MD_RAID456_STRIPE_SHIFT
>> +    int "RAID4/RAID5/RAID6 stripe size shift"
>> +    default "1"
>> +    depends on MD_RAID456
>> +    help
>> +      When set the value as 'N', stripe size will be set as 'N << 9',
>> +      which is a multiple of 4KB.
> 
> If 'N  << 9', then seems you are convert it to sector, do you actually mean 'N << 12'?
> 
>> +
>> +      The default value is 1, that means the default stripe size is
>> +      4096(1 << 9). Just setting as a bigger value when PAGE_SIZE is
>> +      bigger than 4096. In that case, you can set it as 2(8KB),
>> +      4(16K), 16(64K).
> 
> So with the above description, the algorithm should be 2 << 12 = 8KB and so on.
> 
>> +
>> +      When you try to set a big value, likely 16 on arm64 with 64KB
>> +      PAGE_SIZE, that means, you know size of each io that issued to
>> +      raid device is more than 4096. Otherwise just use default value.
>> +
>> +      Normally, using default value can get better performance.
>> +      Only change this value if you know what you are doing.
>> +
>> +
>>   config MD_MULTIPATH
>>       tristate "Multipath I/O support"
>>       depends on BLK_DEV_MD
>> diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
>> index f90e0704bed9..b25f107dafc7 100644
>> --- a/drivers/md/raid5.h
>> +++ b/drivers/md/raid5.h
>> @@ -472,7 +472,9 @@ struct disk_info {
>>    */
>>   #define NR_STRIPES        256
>> -#define STRIPE_SIZE        PAGE_SIZE
>> +#define CONFIG_STRIPE_SIZE    (CONFIG_MD_RAID456_STRIPE_SHIFT << 9)
>> +#define STRIPE_SIZE        \
>> +    (CONFIG_STRIPE_SIZE > PAGE_SIZE ? PAGE_SIZE : CONFIG_STRIPE_SIZE)
> 
> If I am not misunderstand, you need to s/9/12/ above.

Oh yeah, thanks a lot for catching this. Sorry for this obvious error.
It show be 12, then STRIPE_SIZE can be multiple of 4KB, as Liu Song suggested.

Thanks,
Yufen,