Re: [PATCH] deadline io scheduler

Daniel Pittman
2002-09-26T08:22:50Z

On Thu, 26 Sep 2002, Jens Axboe wrote:
> On Wed, Sep 25 2002, Andrew Morton wrote:

[...]

> writes_starved. This controls how many times reads get preferred over
> writes. The default is 2, which means that we can serve two batches of
> reads over one write batch. A value of 4 would mean that reads could
> skip ahead of writes 4 times. A value of 1 would give you 1:1
> read:write, ie no read preference. A silly value of 0 would give you
> write preference, always.

Actually, a value of zero doesn't sound completely silly to me, right
now, since I have been doing a lot of thinking about video capture
recently.

How much is it going to hurt a filesystem like ext[23] if that value is
set to zero while doing large streaming writes -- something like
(almost) uncompressed video at ten to twenty meg a second, for
gigabytes?

This is a situation where, for a dedicated machine, delaying reads
almost forever is actually a valuable thing. At least, valuable until it
stops the writes from being able to proceed.

Daniel

--
The best way to get a bad law repealed is to enforce it strictly.
-- Abraham Lincoln