From: Dan Smith <danms@xxxxxxxxxx>
Subject: Re: dm-userspace (no in-kernel cache version)
Date: Thu, 14 Sep 2006 08:59:15 -0700
> FT> Have you tried SCHED_FIFO?
>
> Not yet, but that is a good suggestion.
>
> FT> By the way, can you upload or post the latest kernel and
> FT> user-space code?
>
> Right now I am working on a version that still uses read()/write(),
> but that does not use a remap cache (in a way very similar to what you
> posted). When I get it close to stable, I'll post it here for
> comments.
I see.
> After reviewing the ringbuffer code more, I'm not sure that it really
> buys you any additional performance (other than 1/3 less syscalls).
> The amount of memory that is copied around seems to be about the
> same.
Well, my code just uses ring buffer and is not tuned yet. As you know,
you can eliminate memory copies easily (I've attached a patch to do
that for dmu_uspace_send_map_req), though maybe memory copies don't
make the large difference. As you said, after having a stable version
without rmap cache, performance tests (write/read vs. ring buffer)
are necessary.
diff --git a/drivers/md/dm-userspace-chardev.c b/drivers/md/dm-userspace-chardev.c
index 5a4b0d3..42172ce 100644
--- a/drivers/md/dm-userspace-chardev.c
+++ b/drivers/md/dm-userspace-chardev.c
@@ -117,12 +117,35 @@ static int dmu_uspace_send_event(struct
int dmu_uspace_send_map_req(struct dmu_device *dev, u64 id, u32 flags, u64 block)
{
- struct dmu_event ev;
+ struct chardev_transport *t = dev->transport_private;
+ struct dmu_ring *ring = &t->tx;
+ struct dmu_event *ev;
+ int err = 0;
+
+ spin_lock(&ring->r_lock);
+
+ ev = dmu_head_event(ring, ring->r_idx);
+ if (!ev->status) {
+
+ ev->type = DM_USERSPACE_MAP_BLOCK_REQ;
+ ev->status = 1;
+ ev->k.map_req.id = id;
+ ev->k.map_req.flags = flags;
+ ev->k.map_req.block = block;
- ev.k.map_req.id = id;
- ev.k.map_req.flags = flags;
- ev.k.map_req.block = block;
- return dmu_uspace_send_event(dev, DM_USERSPACE_MAP_BLOCK_REQ, &ev);
+ mb();
+ dmu_ring_idx_inc(ring);
+ } else
+ err = -EBUSY;
+
+ spin_unlock(&ring->r_lock);
+
+ if (!err) {
+ flush_dcache_page(virt_to_page(ev));
+ wake_up_interruptible(&t->tx_poll_wait);
+ }
+
+ return err;
}
int dmu_uspace_send_map_status(struct dmu_device *dev, u64 id, u32 status)
--
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