Re: [PATCH -mm] [3/3] Add the Elevator I/O scheduler
From: Al Boldi
Date: Fri Aug 04 2006 - 10:43:02 EST
Nate Diller wrote:
> This is the Elevator I/O scheduler. It is a simple one-way elevator,
Thanks for yet another attempt to achieve an efficient 2.6 elevator.
> +static inline char contig_char(struct el_request *e)
You probably meant el_req. Check the rest.
> +static void print_queue(struct request_queue *q, struct el_data *el)
> + struct el_req *e;
> + printel(el);
Should be print_el_data.
Applied against 2.6.17, it boots with this:
io scheduler elevator registered (default)
elevator: forced dispatching is broken (nr_sorted=13), please report this
> +In pure form its largest weakness is starvation of other processes due to
> +one process writing a very large number of contiguous requests (e.g.
> +tarring a very large tar file while other processes are trying to run).
cat /dev/hda > /dev/null starves the rest of the system.
> +The max_contig and max_write tunables are two (imperfect) solutions. They
> +These two tunables are still under construction, but they have proven
> +somewhat useful in practice. Usually, max_contig should be the same size
> +(in bytes) as ra_pages.
It's 0 by default. Setting it to ra_pages prints this:
nate 1977: max_contig went backwards
> + SSTF
> +The SSTF feature was added on a whim. It ignores the tunables, and
> probably +breaks tracing. I didn't ever see it perform better than SCAN,
> but who +knows?
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