On Wed, Jul 19, 2017 at 07:25:41PM -0400, Ujjal Singh wrote:
> We observed performance increase with DMA copy from memory
> to MMIO by changing the interrupt coalescing value to 0.
> The previous set value was projected on the C5xxx Xeon
> platform and no longer holds true. Removing hard coded
> value and providing a tune-able in sysfs in order to allow
> user to tune this on a per channel basis. By default this
> value will be set to 0.
> Example of sysfs variable importing for interrupt coalescing
> value from command line:
> echo 5> /sys/devices/pci0000:00/0000:00:04.0/dma/dma0chan0/
> quickdata/intr_coalesce
>
> Reported-by: Nithin Sujir <nsujir@xxxxxxxxxx>
> Signed-off-by: Ujjal Singh <ujjal.singh@xxxxxxxxx>
> ---
> V2: Addressed Dave's comments:
> > Removed definition INTR_DELAY_REG_LIMIT in hw.h and used
> > existing definition IOAT_INTRDELAY_MASK instead to check
> > interrupt delay limit in sysfs.c
>
> Vinod's comment about ABI doc will come in a different patch
> to add ABI doc for ioatdma.
Sure, but we should send that first and add ABI documentation for this new
file in current patch or part of this series
>
> drivers/dma/ioat/dma.c | 10 +++++++---
> drivers/dma/ioat/dma.h | 3 +++
> drivers/dma/ioat/sysfs.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 52 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/ioat/dma.c b/drivers/dma/ioat/dma.c
> index a371b07..f70cc74 100644
> --- a/drivers/dma/ioat/dma.c
> +++ b/drivers/dma/ioat/dma.c
> @@ -644,9 +644,13 @@ static void __cleanup(struct ioatdma_chan *ioat_chan, dma_addr_t phys_complete)
> mod_timer(&ioat_chan->timer, jiffies + IDLE_TIMEOUT);
> }
>
> - /* 5 microsecond delay per pending descriptor */
> - writew(min((5 * (active - i)), IOAT_INTRDELAY_MASK),
> - ioat_chan->ioat_dma->reg_base + IOAT_INTRDELAY_OFFSET);
> + /* microsecond delay by sysfs variable per pending descriptor */
> + if (ioat_chan->intr_coalesce != ioat_chan->prev_intr_coalesce) {
> + writew(min((ioat_chan->intr_coalesce * (active - i)),
> + IOAT_INTRDELAY_MASK),
> + ioat_chan->ioat_dma->reg_base + IOAT_INTRDELAY_OFFSET);
> + ioat_chan->prev_intr_coalesce = ioat_chan->intr_coalesce;
> + }
> }
>
> static void ioat_cleanup(struct ioatdma_chan *ioat_chan)
> diff --git a/drivers/dma/ioat/dma.h b/drivers/dma/ioat/dma.h
> index a9bc1a1..56200ee 100644
> --- a/drivers/dma/ioat/dma.h
> +++ b/drivers/dma/ioat/dma.h
> @@ -142,11 +142,14 @@ struct ioatdma_chan {
> spinlock_t prep_lock;
> struct ioat_descs descs[2];
> int desc_chunks;
> + int intr_coalesce;
> + int prev_intr_coalesce;
> };
>
> struct ioat_sysfs_entry {
> struct attribute attr;
> ssize_t (*show)(struct dma_chan *, char *);
> + ssize_t (*store)(struct dma_chan *, const char *, size_t);
> };
>
> /**
> diff --git a/drivers/dma/ioat/sysfs.c b/drivers/dma/ioat/sysfs.c
> index cb4a857..3ac677f 100644
> --- a/drivers/dma/ioat/sysfs.c
> +++ b/drivers/dma/ioat/sysfs.c
> @@ -64,8 +64,24 @@ ioat_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
> return entry->show(&ioat_chan->dma_chan, page);
> }
>
> +static ssize_t
> +ioat_attr_store(struct kobject *kobj, struct attribute *attr,
> +const char *page, size_t count)
> +{
> + struct ioat_sysfs_entry *entry;
> + struct ioatdma_chan *ioat_chan;
> +
> + entry = container_of(attr, struct ioat_sysfs_entry, attr);
> + ioat_chan = container_of(kobj, struct ioatdma_chan, kobj);
> +
> + if (!entry->store)
> + return -EIO;
> + return entry->store(&ioat_chan->dma_chan, page, count);
> +}
> +
> const struct sysfs_ops ioat_sysfs_ops = {
> .show = ioat_attr_show,
> + .store = ioat_attr_store,
> };
>
> void ioat_kobject_add(struct ioatdma_device *ioat_dma, struct kobj_type *type)
> @@ -121,11 +137,37 @@ static ssize_t ring_active_show(struct dma_chan *c, char *page)
> }
> static struct ioat_sysfs_entry ring_active_attr = __ATTR_RO(ring_active);
>
> +static ssize_t intr_coalesce_show(struct dma_chan *c, char *page)
> +{
> + struct ioatdma_chan *ioat_chan = to_ioat_chan(c);
> +
> + return sprintf(page, "%d\n", ioat_chan->intr_coalesce);
> +}
> +
> +static ssize_t intr_coalesce_store(struct dma_chan *c, const char *page,
> +size_t count)
> +{
> + int intr_coalesce = 0;
> + struct ioatdma_chan *ioat_chan = to_ioat_chan(c);
> +
> + if (sscanf(page, "%du", &intr_coalesce) != -1) {
> + if ((intr_coalesce < 0) ||
> + (intr_coalesce > IOAT_INTRDELAY_MASK))
> + return -EINVAL;
> + ioat_chan->intr_coalesce = intr_coalesce;
> + }
> +
> + return count;
> +}
> +
> +static struct ioat_sysfs_entry intr_coalesce_attr = __ATTR_RW(intr_coalesce);
> +
> static struct attribute *ioat_attrs[] = {
> &ring_size_attr.attr,
> &ring_active_attr.attr,
> &ioat_cap_attr.attr,
> &ioat_version_attr.attr,
> + &intr_coalesce_attr.attr,
> NULL,
> };
>
>
--
~Vinod
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