Re: [patch] voluntary-preempt-2.6.8-rc2-J4

Ingo Molnar
2004-07-27T08:01:13Z

[i've sent a second patch too since the first version.]

* Jens Axboe <axboe@suse.de> wrote:

> I don't like it. First of all, the implementation really should drain
> the queue first, then set max value before allowing people to queue
> more io. The queue lock doesn't help here, readers don't even attempt
> to serialize access to max_sectors.

why should the queue be drained? There might be a few leftover big
requests, but these are not a problem.

> Secondly, I don't like the concept of exposing this value. If you want
> to do something like this, we must split the value into two like
> proposed (and patched) some months ago into a hardware and user value.

yes, agreed - that's what the second patch does.

> I don't see why we can't just drop ata48 default value to 256kb
> instead. There's very little command over head on ide, I bet the
> majority of the change in performance when playing with 256kb vs
> 1024kb is not the command overhead itself, rather things like
> read-ahead that could be more intelligent.

256kb isnt enough from a latency POV either - and if a user wants some
extreme setting like 16KB per request why not allow it? Especially since
these tunables cause zero runtime overhead.

Ingo