Priorities for I/O

[Kurt Garloff]

--zS7rBR6csb6tI2e1
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Hi Jens,

one of the shortcomings of Linux process priority system is that it only
affects CPU resources (and even those are not affected strongly enough for
some applications).=20
As soon as processes waits for I/O, they are all equal.

I wonder how difficult it was to just add priorities to your I/O scheduler.
Basically, I think everything is there: You sort requests already and we
have deadlines. For sorting scores are used.
So the idea is: Why not just give I/O submitted on behalf of -19 processes
(and RT) some higher score and a shorter deadline than +19 ones?
Probably, it would only affect reads, as there we have the processes wait
on them; writes are often triggered asynchronously anyway.

This should have the effects that we want: When there's no fight for I/O
bandwidth, everybody just gets maximum performance as the I/O scheduler's
queue will be short. As soon as processes fight for reads, unniced processes
have a higher chance of getting served first.

Just think of nightly updatedb on a webserver for a real-world example why
this may matter.

Looks like something not too difficult to do, but my current knowledge on
2.5 code is somewhat sparse :-(

Regards,
--=20
Kurt Garloff  <[e-mail]>                          Eindhoven, NL
GPG key: See mail header, key servers                        SuSE Labs
SuSE Linux AG, Nuernberg, DE                            SCSI, Security

--zS7rBR6csb6tI2e1
Content-Type: application/pgp-signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.7 (GNU/Linux)

iD8DBQE9s6wkxmLh6hyYd04RAl8OAKCAaWpz82ZBeqtiAFewJM3IrSHEMQCgkokS
cyzk5FRuXZ7MaifCiSd9nwg=
=HuCi
-----END PGP SIGNATURE-----

--zS7rBR6csb6tI2e1--