Increase st_blksize to 64k

Brian Ford
Wed Jan 3 15:56:00 GMT 2007

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 :

...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.

Brian Ford
Lead Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained crew...

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