On Tuesday October 6, dan.j.williams@xxxxxxxxx wrote:
> >From 0496c92cf6ac1f4f7dde6d416707988991d87d41 Mon Sep 17 00:00:00 2001
> From: Dan Williams <dan.j.williams@xxxxxxxxx>
> Date: Sat, 3 Oct 2009 13:47:05 -0700
> Subject: [PATCH] md/raid456: downlevel multicore operations to raid_run_ops
>
> The percpu conversion allowed a straightforward handoff of stripe
> processing to the async subsytem that initially showed some modest gains
> (+4%). However, this model is too simplistic and leads to stripes
> bouncing between raid5d and the async thread pool for every invocation
> of handle_stripe(). As reported by Holger this can fall into a
> pathological situation severely impacting throughput (6x performance
> loss).
>
> By downleveling the parallelism to raid_run_ops the pathological
> stripe_head bouncing is eliminated. This version still exhibits an
> average 11% throughput loss for:
>
> mdadm --create /dev/md0 /dev/sd[b-q] -n 16 -l 6
> echo 1024 > /sys/block/md0/md/stripe_cache_size
> dd if=/dev/zero of=/dev/md0 bs=1024k count=2048
>
> ...but the results are at least stable and can be used as a base for
> further multicore experimentation.
Thanks.
One little change needed:
> static int grow_one_stripe(raid5_conf_t *conf)
> {
> struct stripe_head *sh;
> @@ -1213,6 +1243,9 @@ static int grow_one_stripe(raid5_conf_t *conf)
> memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
> sh->raid_conf = conf;
> spin_lock_init(&sh->lock);
> + #ifdef CONFIG_MULTICORE_RAID456
> + init_waitqueue_head(&sh->ops.wait_for_ops);
> + #endif
>
> if (grow_buffers(sh, conf->raid_disks)) {
> shrink_buffers(sh, conf->raid_disks);
This addition is needed in resize_stripes too.
NeilBrown
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