Date: Wed, 1 Feb 2006 09:18:25 +0900 From: Dipjyoti Saikia <dipjyoti.saikia@gmail.com> To: Bharma Ji <bharmaji@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: How to pin a userland page in memory(avoid copyin and copyout) Message-ID: <dcbc809d0601311618y5faa63dds72bcc0d5fa4bcc32@mail.gmail.com> In-Reply-To: <67beabb0601301146h6c5034fao998bf573f1e89613@mail.gmail.com> References: <67beabb0601301146h6c5034fao998bf573f1e89613@mail.gmail.com>
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On 1/31/06, Bharma Ji <bharmaji@gmail.com> wrote:
>
> Hi
> I am trying to explore the option avoiding copyin and copyout when mode
> switches from user to kernel and vice versa. One way to achieve this, as =
I
> understand, is to make the memory address (which contain the data to be
> copied) non pageable. Then just pass the addresses to the kernel and the
> data will be used directly from the userland page. Is there already some
> example code / standard way to do this?
>
> Also is there any way one can determine the amount of time / performance
> hit
> (CPU %)that happening on a given process due to the copyin and copyout. I
> want to understand how much performance gain one can gain if I am able to
> remove copyin/copyout.
>
> This may give some pointers :
kern/sys_pipe.c
-->pipe_build_write_buffer()
I was working on pipe implementation in BSD derivative of 4.10 branch and
remember the same concept of pinning the user space buffer for bypassing
kernel buffer.
Thanks,
Dip
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