On 06/26/2017 09:44 AM, Dave Jiang wrote:
> On 06/23/2017 05:00 PM, 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>
>
> Acked-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Looks like I missed one thing. You don't need to introduce
INTR_DELAY_REG_LIMIT. You can just use IOAT_INTRDELAY_MASK which is
already there.
>
>> ---
>> drivers/dma/ioat/dma.c | 10 +++++++---
>> drivers/dma/ioat/dma.h | 3 +++
>> drivers/dma/ioat/hw.h | 1 +
>> drivers/dma/ioat/sysfs.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>> 4 files changed, 53 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/hw.h b/drivers/dma/ioat/hw.h
>> index abcc51b..6cd540c 100644
>> --- a/drivers/dma/ioat/hw.h
>> +++ b/drivers/dma/ioat/hw.h
>> @@ -72,6 +72,7 @@
>> #define IOAT_VER_3_2 0x32 /* Version 3.2 */
>> #define IOAT_VER_3_3 0x33 /* Version 3.3 */
>>
>> +#define INTR_DELAY_REG_LIMIT 0x3fff
>>
>> int system_has_dca_enabled(struct pci_dev *pdev);
>>
>> diff --git a/drivers/dma/ioat/sysfs.c b/drivers/dma/ioat/sysfs.c
>> index cb4a857..d7df044 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 > INTR_DELAY_REG_LIMIT))
>> + 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,
>> };
>>
>>
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