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From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
Date: Mon, 08 Nov 2004 11:49:07 +0100
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Subject: [HEADSUP]  Please help test device vnode bypass!
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Please test this feature.

Even better, help test the perforce branch phk_bufwork if you can.

Poul-Henning

In message <200411081046.iA8AklqT003808@repoman.freebsd.org>, Poul-Henning Kamp
 writes:
>phk         2004-11-08 10:46:47 UTC
>
>  FreeBSD src repository
>
>  Modified files:
>    sys/fs/devfs         devfs_vnops.c 
>  Log:
>  Add optional device vnode bypass to DEVFS.
>  
>  The tunable vfs.devfs.fops controls this feature and defaults to off.
>  
>  When enabled (vfs.devfs.fops=1 in loader), device vnodes opened
>  through a filedescriptor gets a special fops vector which instead
>  of the detour through the vnode layer goes directly to DEVFS.
>  
>  Amongst other things this allows us to run Giant free read/write to
>  device drivers which have been weaned off D_NEEDGIANT.
>  
>  Currently this means /dev/null, /dev/zero, disks, (and maybe the
>  random stuff ?)
>  
>  On a 700MHz K7 machine this doubles the speed of
>          dd if=/dev/zero of=/dev/null bs=1 count=1000000
>  
>  This roughly translates to shaving 2usec of each read/write syscall.
>  
>  The poll/kqfilter paths need more work before they are giant free,
>  this work is ongoing in p4::phk_bufwork
>  
>  Please test this and report any problems, LORs etc.
>  
>  Revision  Changes    Path
>  1.82      +287 -0    src/sys/fs/devfs/devfs_vnops.c
>

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.