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Date: Thu, 15 Nov 2012 11:09:48 -0800
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Subject: Re: ZERO_REGION_SIZE
From: Adrian Chadd <adrian@freebsd.org>
To: Alan Cox <alc@rice.edu>
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Cc: "Jayachandran C." <jchandra@freebsd.org>, mips@freebsd.org
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Alan, would you like me to send you some MIPS hardwarE?



Adrian


On 15 November 2012 10:25, Alan Cox <alc@rice.edu> wrote:
> Given the possibility of L1 cache aliasing on some (many?) MIPS
> processors, I think that you, i.e., MIPS users, should evaluate the
> performance effects of the following change:
>
> Index: mips/include/vmparam.h
> ===================================================================
> --- mips/include/vmparam.h      (revision 243091)
> +++ mips/include/vmparam.h      (working copy)
> @@ -190,6 +190,6 @@
>   */
>  #define        VM_NFREEORDER           9
>
> -#define        ZERO_REGION_SIZE        (64 * 1024)     /* 64KB */
> +#define        ZERO_REGION_SIZE        4096
>
>  #endif /* !_MACHINE_VMPARAM_H_ */
>
> You can quantify the impact with a simple test like:
>
> dd if=/dev/zero of=/dev/null bs=<64 or 128>k count=<something non-trivial>
>
> If possible, please use a kernel without WITNESS or INVARIANTS.
>
> Alan
>
> P.S. I would also be curious how setting this to 8192 would perform.
>