"Drivers have been made to behave when using a bigger than 128KB maximum IO transfer size"

Wojciech Puchar wojtek at wojtek.tensor.gdynia.pl
Wed May 14 01:15:15 PDT 2014

will do some tests in weekend

On Sun, 11 May 2014, Francois Tigeot wrote:

> On Sun, May 11, 2014 at 12:19:57PM +0200, Wojciech Puchar wrote:
>> How to turn in on in dragonfly? i mean setting maximum disk I/O to 2 or
>> 4MB - same as i do in FreeBSD to get large performance gain on big files.
>> in FreeBSD
>> options         MAXPHYS=2097152 (or twice that)
>> options         DFLTPHYS=262144
> You could try changing the value of MAXPHYS in sys/cpu/${ARCH}/include/param.h
> MAXPHYS, the maximum allowed I/O size is still capped at 64KB (i386) or 128KB
> (x86_64/amd64) by default.
> I experimented for a while with the ahci driver; bigger values helped to
> increase linear (dd) performance by up to 20% with fast SSDs but it was unclear
> at the time if it would have improved regular filesystem operations.
> Even though all storage drivers compile fine with bigger MAXPHYS values it's
> also possible some will have issues at runtime.
> -- 
> Francois Tigeot

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