Date: Wed, 22 Nov 2006 20:17:51 -0500 From: Kris Kennaway <kris@obsecurity.org> To: Dieter <freebsd@sopwith.solgatos.com> Cc: freebsd-questions@freebsd.org Subject: Re: processes not getting fair share of available disk I/O (was: Re: TCP parameters and interpreting tcpdump output ) Message-ID: <20061123011751.GA45406@xor.obsecurity.org> In-Reply-To: <200611221902.TAA14770@sopwith.solgatos.com> References: <20061122165238.GA37819@xor.obsecurity.org> <200611221902.TAA14770@sopwith.solgatos.com>
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--mP3DRpeJDSE+ciuQ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Nov 22, 2006 at 11:02:54AM +0000, Dieter wrote: > In message <20061122165238.GA37819@xor.obsecurity.org>, Kris Kennaway wri= tes: >=20 > > > > I'm surprised that you're seeing that much of a "hang". Even if th= e di=3D > > sks > > > > are busy, the system should slow down all disk processes equally, s= o no > > > > one process "blocks", but they're all a little slower. > > >=3D20 > > > I collected a bit of data: > > >=3D20 > > > While copying a large file from disk1 to disk2, > > >=3D20 > > > time ls on a small directory on disk3 (not cached in memory) > > >=3D20 > > > real 0m0.032s > > > user 0m0.000s > > > sys 0m0.003s > > >=3D20 > > > time ls on a small directory on disk2 > > >=3D20 > > > real 4m51.911s > > > user 0m0.000s > > > sys 0m0.002s > > >=3D20 > > > I expect access to a busy disk to take longer, but 5 minutes is > > > a bit much. And that's the root directory of the filesystem, > > > it didn't have to follow a long chain of directories to get there. > > >=3D20 > > > Sometimes I see long delays when accessing disk3, but it is > > > behaving at the moment. > >=20 > > ls still has to acquire a number of locks in order to be sure that the > > contents of the directory aren't changing. If there are lots of other > > processes all competing for these locks, it will be slow. It looks > > like that's the case on your system, although details of your workload > > have been trimmed from your email. >=20 > In telnet window 1: >=20 > cd /disk1/ > cp -ip very_big_file /disk2/bar/ (the workload) >=20 > In telnet window 2: >=20 > time ls /disk3/foo1/ (make sure time and ls are cached in memory) > time ls /disk3/foo2/ (see timing numbers above) > time ls /disk2/ (see timing numbers above) >=20 > The /disk2/ directory is small, only contains 3 directories and .snap >=20 > Would the cp into /disk2/bar/ lock the /disk2/ directory? It shouldn't do. What scheduler are you using? Kris --mP3DRpeJDSE+ciuQ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQFFZPa/Wry0BWjoQKURArEdAJ43LEv5rl7/RIf8VevDcwfXcJhRdQCgvjzh /rfxDl6M2NDXh3ctXl/m7UA= =AxZ1 -----END PGP SIGNATURE----- --mP3DRpeJDSE+ciuQ--
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