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SubjectRe: AIO!!
Date
On Tuesday 11 October 2005 08:04, Karthik Sarangan wrote:
> > 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

Why do you constantly shout?

> ------------------
> 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?

I suspect you did not do some research first.

> 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 !! --

Most probably bug in your program.

> Buffer cache does not come into consideration.
>
> Does this mean that the SCSI lower layer (aic79xx) can transfer data
> only upto 512 KB?

It means that you are in dire need of reading this:

http://www.catb.org/~esr/faqs/smart-questions.html

--
vda
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