Re: AIO!!

[Karthik Sarangan <karthiks@cdac.in>]

> Benjamin LaHaise wrote:
> O_DIRECT buffers must be aligned on block sized boundaries (minimum 512 
> bytes).  Check the actual return code from the aiocb and you'll find that 
> it is likely -EINVAL, no -EINPROGRESS.  See the man page for 
> posix_memalign() to properly align the pointer.

EEP!! I forgot all about buffer alignment!! Thanks for pointing it out

:)

------------------

Two more questions.

1. Is aio_fsync of any use while 'aio_read'ing and 'aio_write'ing to
   a 'raw' device or a '/dev/sdb' with O_DIRECT?

2. I have an Ultra320 SCSI disk whose datasheet says it has a max.
   possible throughput of 78MBps

   I did a 'aio_write' onto '/dev/sdb' with O_DIRECT.
   Following are some throughput values.

   Buffer for IO   |  Avg Speed
   (in KBytes)     |
   ----------------O-----------
   Upto 512KB      |  69MBps
   1024KB          |  125MBps
   2048KB          |  250MBps
   4096KB          |  500MBps
   8192KB          |  1GBps		-- What the !! --

   Buffer cache does not come into consideration.

   Does this mean that the SCSI lower layer (aic79xx) can transfer data
   only upto 512 KB?

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