Date: Mon, 8 Nov 2004 10:46:47 +0000 (UTC) From: Poul-Henning Kamp <phk@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/fs/devfs devfs_vnops.c Message-ID: <200411081046.iA8AklqT003808@repoman.freebsd.org>
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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
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