[Lustre-devel] Readx issue

Peter Braam Peter.Braam at Sun.COM
Thu Aug 21 22:02:30 PDT 2008

Very exciting.   I have cc'd lustre-devel, because this is exciting.


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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