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Message-ID: <20071120125047.GC10127@Krystal>
Date: Tue, 20 Nov 2007 07:50:47 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: clameter@....com
Cc: ak@...e.de, akpm@...ux-foundation.org, travis@....com,
linux-kernel@...r.kernel.org
Subject: Re: [rfc 23/45] cpu alloc: dmaengine conversion
* clameter@....com (clameter@....com) wrote:
> Convert DMA engine to use CPU_xx operations. This also removes the use of local_t
> from the dmaengine.
>
> Signed-off-by: Christoph Lameter <clameter@....com>
> ---
> drivers/dma/dmaengine.c | 38 ++++++++++++++------------------------
> include/linux/dmaengine.h | 16 ++++++----------
> 2 files changed, 20 insertions(+), 34 deletions(-)
>
> Index: linux-2.6/drivers/dma/dmaengine.c
> ===================================================================
> --- linux-2.6.orig/drivers/dma/dmaengine.c 2007-11-19 15:45:06.009390961 -0800
> +++ linux-2.6/drivers/dma/dmaengine.c 2007-11-19 15:59:59.894744662 -0800
> @@ -84,7 +84,7 @@ static ssize_t show_memcpy_count(struct
> int i;
>
> for_each_possible_cpu(i)
> - count += per_cpu_ptr(chan->local, i)->memcpy_count;
> + count += CPU_PTR(chan->local, i)->memcpy_count;
>
> return sprintf(buf, "%lu\n", count);
> }
> @@ -96,7 +96,7 @@ static ssize_t show_bytes_transferred(st
> int i;
>
> for_each_possible_cpu(i)
> - count += per_cpu_ptr(chan->local, i)->bytes_transferred;
> + count += CPU_PTR(chan->local, i)->bytes_transferred;
>
> return sprintf(buf, "%lu\n", count);
> }
> @@ -110,10 +110,8 @@ static ssize_t show_in_use(struct class_
> atomic_read(&chan->refcount.refcount) > 1)
> in_use = 1;
> else {
> - if (local_read(&(per_cpu_ptr(chan->local,
> - get_cpu())->refcount)) > 0)
> + if (_CPU_READ(chan->local->refcount) > 0)
> in_use = 1;
> - put_cpu();
> }
>
> return sprintf(buf, "%d\n", in_use);
> @@ -226,7 +224,7 @@ static void dma_chan_free_rcu(struct rcu
> int bias = 0x7FFFFFFF;
> int i;
> for_each_possible_cpu(i)
> - bias -= local_read(&per_cpu_ptr(chan->local, i)->refcount);
> + bias -= _CPU_READ(chan->local->refcount);
> atomic_sub(bias, &chan->refcount.refcount);
> kref_put(&chan->refcount, dma_chan_cleanup);
> }
> @@ -372,7 +370,8 @@ int dma_async_device_register(struct dma
>
> /* represent channels in sysfs. Probably want devs too */
> list_for_each_entry(chan, &device->channels, device_node) {
> - chan->local = alloc_percpu(typeof(*chan->local));
> + chan->local = CPU_ALLOC(typeof(*chan->local),
> + GFP_KERNEL | __GFP_ZERO);
> if (chan->local == NULL)
> continue;
>
> @@ -385,7 +384,7 @@ int dma_async_device_register(struct dma
> rc = class_device_register(&chan->class_dev);
> if (rc) {
> chancnt--;
> - free_percpu(chan->local);
> + CPU_FREE(chan->local);
> chan->local = NULL;
> goto err_out;
> }
> @@ -413,7 +412,7 @@ err_out:
> kref_put(&device->refcount, dma_async_device_cleanup);
> class_device_unregister(&chan->class_dev);
> chancnt--;
> - free_percpu(chan->local);
> + CPU_FREE(chan->local);
> }
> return rc;
> }
> @@ -488,11 +487,8 @@ dma_async_memcpy_buf_to_buf(struct dma_c
> tx->tx_set_dest(addr, tx, 0);
> cookie = tx->tx_submit(tx);
>
> - cpu = get_cpu();
> - per_cpu_ptr(chan->local, cpu)->bytes_transferred += len;
> - per_cpu_ptr(chan->local, cpu)->memcpy_count++;
> - put_cpu();
> -
> + __CPU_ADD(chan->local->bytes_transferred, len);
> + __CPU_INC(chan->local->memcpy_count);
I am wondering about the impact of the preempt disable removal here. It
means that there is a statistically low probability that we will be
moved to a different CPU between the bytes_transferred and the
memcpy_count increments. I hope nobody relies on the fact that the
per-cpu counts should match perfectly...
> return cookie;
> }
> EXPORT_SYMBOL(dma_async_memcpy_buf_to_buf);
> @@ -532,11 +528,8 @@ dma_async_memcpy_buf_to_pg(struct dma_ch
> tx->tx_set_dest(addr, tx, 0);
> cookie = tx->tx_submit(tx);
>
> - cpu = get_cpu();
> - per_cpu_ptr(chan->local, cpu)->bytes_transferred += len;
> - per_cpu_ptr(chan->local, cpu)->memcpy_count++;
> - put_cpu();
> -
> + _CPU_ADD(chan->local->bytes_transferred, len);
> + _CPU_INC(chan->local->memcpy_count);
> return cookie;
> }
> EXPORT_SYMBOL(dma_async_memcpy_buf_to_pg);
> @@ -578,11 +571,8 @@ dma_async_memcpy_pg_to_pg(struct dma_cha
> tx->tx_set_dest(addr, tx, 0);
> cookie = tx->tx_submit(tx);
>
> - cpu = get_cpu();
> - per_cpu_ptr(chan->local, cpu)->bytes_transferred += len;
> - per_cpu_ptr(chan->local, cpu)->memcpy_count++;
> - put_cpu();
> -
> + _CPU_ADD(chan->local->bytes_transferred, len);
> + _CPU_INC(chan->local->memcpy_count);
> return cookie;
> }
> EXPORT_SYMBOL(dma_async_memcpy_pg_to_pg);
> Index: linux-2.6/include/linux/dmaengine.h
> ===================================================================
> --- linux-2.6.orig/include/linux/dmaengine.h 2007-11-19 15:45:06.017390185 -0800
> +++ linux-2.6/include/linux/dmaengine.h 2007-11-19 15:56:26.814390333 -0800
> @@ -102,13 +102,13 @@ typedef struct { DECLARE_BITMAP(bits, DM
>
> /**
> * struct dma_chan_percpu - the per-CPU part of struct dma_chan
> - * @refcount: local_t used for open-coded "bigref" counting
> + * @refcount: int used for open-coded "bigref" counting
> * @memcpy_count: transaction counter
> * @bytes_transferred: byte counter
> */
>
> struct dma_chan_percpu {
> - local_t refcount;
> + int refcount;
> /* stats */
> unsigned long memcpy_count;
> unsigned long bytes_transferred;
> @@ -149,20 +149,16 @@ static inline void dma_chan_get(struct d
> {
> if (unlikely(chan->slow_ref))
> kref_get(&chan->refcount);
> - else {
> - local_inc(&(per_cpu_ptr(chan->local, get_cpu())->refcount));
> - put_cpu();
> - }
> + else
> + _CPU_INC(chan->local->refcount);
> }
>
> static inline void dma_chan_put(struct dma_chan *chan)
> {
> if (unlikely(chan->slow_ref))
> kref_put(&chan->refcount, dma_chan_cleanup);
> - else {
> - local_dec(&(per_cpu_ptr(chan->local, get_cpu())->refcount));
> - put_cpu();
> - }
> + else
> + _CPU_DEC(chan->local->refcount);
> }
>
> /*
>
> --
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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