Re: Re: [patch]raid5: fix directio regression

["Jianpeng Ma" <majianpeng@gmail.com>]

On 2012-08-08 10:58 Shaohua Li <shli@kernel.org> Wrote:
>2012/8/7 Jianpeng Ma <majianpeng@gmail.com>:
>> On 2012-08-07 13:32 Shaohua Li <shli@kernel.org> Wrote:
>>>2012/8/7 Jianpeng Ma <majianpeng@gmail.com>:
>>>> On 2012-08-07 11:22 Shaohua Li <shli@kernel.org> Wrote:
>>>>>My directIO randomwrite 4k workload shows a 10~20% regression caused by commit
>>>>>895e3c5c58a80bb. directIO usually is random IO and if request size isn't big
>>>>>(which is the common case), delay handling of the stripe hasn't any advantages.
>>>>>For big size request, delay can still reduce IO.
>>>>>
>>>>>Signed-off-by: Shaohua Li <shli@fusionio.com>
>> [snip]
>>>>>--
>>>> May be used size to judge is not a good method.
>>>> I firstly sended this patch, only want to control direct-write-block,not for reqular file.
>>>> Because i think if someone used direct-write-block for raid5,he should know the feature of raid5 and he can control
>>>> for write to full-write.
>>>> But at that time, i did know how to differentiate between regular file and block-device.
>>>> I thik we should do something to do this.
>>>
>>>I don't think it's possible user can control his write to be a
>>>full-write even for
>>>raw disk IO. Why regular file and block device io matters here?
>>>
>>>Thanks,
>>>Shaohua
>> Another problem is the size. How to judge the size is large or not?
>> A syscall write is a dio and a dio may be split more bios.
>> For my workload, i usualy write chunk-size.
>> But your patch is judge by bio-size.
>
>I'd ignore workload which does sequential directIO, though
>your workload is, but I bet no real workloads are. So I'd like
Sorry,my explain maybe not corcrect. I write data once which size is almost chunks-size * devices,in order to full-write 
and as possible as to no pre-read operation.
>only to consider big size random directio. I agree the size
>judge is arbitrary. I can optimize it to be only consider stripe
>which hits two or more disks in one bio, but not sure if it's
>worthy doing. Not ware big size directio is common, and even
>is, big size request IOPS is low, a bit delay maybe not a big
>deal.
If add a acc_time for 'striep_head' to control?
When get_active_stripe() is ok, update acc_time.
For some time, stripe_head did not access and it shold pre-read.