On Fri, Mar 20, 2015 at 04:53:42PM -0700, Xin Li wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA512 > > On 03/20/15 14:02, Mike Tancsa wrote: > > OK, I think I found where the RELENG_10 performance loss happened. > > It seems > > https://lists.freebsd.org/pipermail/svn-src-stable-10/2015-March/004778.html > > > > is the issue. > > > > Testing with a kernel from r279796 I get 76-77Mb of throughput. > > With r279848 it drops to about 60Mb > > Hrm, looking at 'diffgraph.svg', it suggest that writing through devfs > have incurred a tax on writev(2), which is basically this codepath, if > my reading is correct, in sys/fs/devfs/devfs.c: > > 1676 static int > 1677 devfs_write_f(struct file *fp, struct uio *uio, struct ucred > *cred, > 1678 int flags, struct thread *td) > 1679 { > ... > 1703 if (uio->uio_resid != resid || (error == 0 && resid != > 0)) { > 1704 vfs_timestamp(&dev->si_ctime); > 1705 dev->si_mtime = dev->si_ctime; > 1706 } > > Further looking at the code, in devfs vfs_timestamp() is also called > when reading from a device node. When the setting was 0, the code > would return time_second directly instead of attempting to read the > timestamp. > > For the purpose of devfs, does it make sense to bump timestamps like > normal filesystems for each read/write operation? Looks like Mac OS X > will bump timestamps for each operation but Debian don't.
First question is, what timecounter hardware is used. I would accept some slowdown from hardware like HPET, but it is indeed surprising if caused by TSC. _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[email protected]"
