[Lustre-devel] Readx issue

Peter Bojanic Peter.Bojanic at Sun.COM
Fri Aug 22 11:50:39 PDT 2008

Wang Di,

Can you produce some sample benchmarks that show IO performance with  
and without readx? That would be very helpful to understand the  
benefits of using the new API.


On 22-Aug-08, at 2:02 AM, Peter Braam wrote:

> Very exciting.   I have cc'd lustre-devel, because this is exciting.
> Peter
> On 8/21/08 10:56 PM, "Tom.Wang" <Tom.Wang at Sun.COM> wrote:
>> Hello,
>> Readx/writex code has been done based on HEAD. (ACC-sm has been  
>> passed)
>> Since the target here is to issue the vector read extents req  
>> parallel,
>> so I chosed to implement that by read-ahead
>> group io, which is async and parallel. And also by this way, it  
>> will not
>> touch other module of lustre.
>> In vector read-ahead, each read request will control their read- 
>> ahead by
>> itself, instead of by the current read-ahead window, where multi
>> read-threads(for the same file) use single read ahead window.
>> Because current read-ahead
>>  1)Use a single continuous RA window to control the read ahead.
>>  2)The read-ahead moves forward according to the global RA window(for
>> all the read threads of this file), so it tries to favour all the  
>> read
>> threads of the file,
>> This algorithm is not very nice for vector read-ahead. because
>> 1) It is hard to manage the multi discontinuous read-ahead window,  
>> for
>> example add/remove the extents from the window will be very subtle.
>> 2) It is hard to favour all the vector read-threads(for the file)  
>> by 1
>> single read-ahead window.
>> So I let each vector read threads control their read-ahead  
>> themselves,
>> which will make implementation very easy, and it will also not touch
>> original read-ahead algorithm for non-vector read.  If you disagree
>> about this, please tell me.
>> So all the implementation(readx,writex) actually did not touch other
>> module at all currently.  I will ask some senior ppl to inspect the
>> patch. I do not know the further plan with CERN, will they try this
>> current release or HEAD? If they want try it in current release. Is  
>> that
>> ok I could land it in b1_6 or b1_8 after it pass inspection? Please  
>> advise.
>> Thanks
>> WangDi

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