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Disable timestamping on devfs read/write operations by default.

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Currently we update timestamps unconditionally when doing read or
write operations.  This may slow things down on hardware where
reading timestamps is expensive (e.g. HPET, because of the default
vfs.timestamp_precision setting is nanosecond now) with limited
benefit.

A new sysctl variable, vfs.devfs.dotimes is added, which can be
set to non-zero value when the old behavior is desirable.

Differential Revision:	https://reviews.freebsd.org/D2104
Reported by:	Mike Tancsa <mike sentex net>
Reviewed by:	kib
Relnotes:	yes
Sponsored by:	iXsystems, Inc.
MFC after:	2 weeks
This commit is contained in:
delphij 2015-03-21 01:14:11 +00:00
parent f0d9946f04
commit 041657da93
2 changed files with 12 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sys/fs/devfs/devfs_devs.c
View File

@ -61,7 +61,7 @@ static MALLOC_DEFINE(M_DEVFS2, "DEVFS2", "DEVFS data 2");
static MALLOC_DEFINE(M_DEVFS3, "DEVFS3", "DEVFS data 3");
static MALLOC_DEFINE(M_CDEVP, "DEVFS1", "DEVFS cdev_priv storage");
static SYSCTL_NODE(_vfs, OID_AUTO, devfs, CTLFLAG_RW, 0, "DEVFS filesystem");
SYSCTL_NODE(_vfs, OID_AUTO, devfs, CTLFLAG_RW, 0, "DEVFS filesystem");
static unsigned devfs_generation;
SYSCTL_UINT(_vfs_devfs, OID_AUTO, generation, CTLFLAG_RD,

13
sys/fs/devfs/devfs_vnops.c
View File

@ -57,6 +57,7 @@
#include <sys/proc.h>
#include <sys/stat.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/time.h>
#include <sys/ttycom.h>
#include <sys/unistd.h>
@ -79,6 +80,12 @@ SX_SYSINIT(clone_drain_lock, &clone_drain_lock, "clone events drain lock");
struct mtx cdevpriv_mtx;
MTX_SYSINIT(cdevpriv_mtx, &cdevpriv_mtx, "cdevpriv lock", MTX_DEF);
SYSCTL_DECL(_vfs_devfs);
static int devfs_dotimes;
SYSCTL_INT(_vfs_devfs, OID_AUTO, dotimes, CTLFLAG_RW,
&devfs_dotimes, 0, "Update timestamps on DEVFS");
static int
devfs_fp_check(struct file *fp, struct cdev **devp, struct cdevsw **dswp,
int *ref)
@ -1221,7 +1228,8 @@ devfs_read_f(struct file *fp, struct uio *uio, struct ucred *cred,
foffset_lock_uio(fp, uio, flags | FOF_NOLOCK);
error = dsw->d_read(dev, uio, ioflag);
if (uio->uio_resid != resid || (error == 0 && resid != 0))
if (devfs_dotimes &&
(uio->uio_resid != resid || (error == 0 && resid != 0)))
vfs_timestamp(&dev->si_atime);
td->td_fpop = fpop;
dev_relthread(dev, ref);
@ -1700,7 +1708,8 @@ devfs_write_f(struct file *fp, struct uio *uio, struct ucred *cred,
resid = uio->uio_resid;
error = dsw->d_write(dev, uio, ioflag);
if (uio->uio_resid != resid || (error == 0 && resid != 0)) {
if (devfs_dotimes &&
(uio->uio_resid != resid || (error == 0 && resid != 0))) {
vfs_timestamp(&dev->si_ctime);
dev->si_mtime = dev->si_ctime;
}