Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

Jens Axboe
2004-07-20T14:18:44Z

On Tue, Jul 20 2004, Ingo Molnar wrote:
> > How much I/O do you allow to be in flight at once? It seems like by
> > decreasing the maximum size of I/O that you handle in one interrupt
> > you could improve this quite a bit. Disk throughput is good enough,
> > anyone in the real world who would feel a 10% hit would just throw
> > hardware at the problem.
>
> i'm not sure whether this particular value (max # of sg-entries per IO
> op) is runtime tunable. Jens? Might make sense to enable elvtune-alike
> tunability of this value.

elvtune is long dead :-)

it's not tweakable right now, but if you wish to experiment you just
need to add a line to ide-disk.c:idedisk_setup() - pseudo patch:

+ blk_queue_max_sectors(drive->queue, 32);
+
printk("%s: max request size: %dKiB\n", drive->name, drive->queue->max_sectors / 2);

/* Extract geometry if we did not already have one for the drive */

above will limit max request to 16kb, experiment as you see fit.

--
Jens Axboe