Re: Increase st_blksize to 64k

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Jan  3 09:56, Brian Ford wrote:
> On Wed, 3 Jan 2007, Corinna Vinschen wrote:
> 
> > So it appears to make much sense to set the blocksize to 64K.
> 
> blocksize is not really the proper term here as it is very confusing.
> Preferred or optimal I/O size is a better choice in my opinion.
> 
> > The only question would be whether to use getpagesize() or a hard coded
> > value.  It seems to me that the 64K allocation granularity and using 64K
> > as buffer size in disk I/O coincide so I tend to agree that it makes
> > sort of sense to use getpagesize at this point.
> 
> More supporting evidence from
> http://research.microsoft.com/BARC/Sequential_IO/Win2K_IO_MSTR_2000_55.doc :
> 
> ...each (8KB) buffered random write is actually a 64KB random read and
> then an 8KB write.  When a buffered write request is received, the cache
> manager memory maps a 256KB view into the file. It then pages in the 64KB
> frame continuing the changed 8KB, and modifies that 8KB of data.  This
> means that for each buffered random write includes one or more 64KB reads.
> The right side of Figure 11 shows this 100% IO penalty.

Interesting.  I just applied a patch along the lines of your patch and
what we discussed in this thread.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat