Adding DMA support for pmem blk reads. This provides signficant CPU
reduction with large memory reads with good performance. DMAs are triggered
with test against bio_multiple_segment(), so the small I/Os (4k or less?)
are still performed by the CPU in order to reduce latency. By default
the pmem driver will be using blk-mq with DMA.
Numbers below are measured against pmem simulated via DRAM using
memmap=NN!SS. DMA engine used is the ioatdma on Intel Skylake Xeon
platform. Keep in mind the performance for actual persistent memory
will differ.
Fio 2.21 was used.
64k: 1 task queuedepth=1
CPU Read: 7631 MB/s 99.7% CPU DMA Read: 2415 MB/s 54% CPU
CPU Write: 3552 MB/s 100% CPU DMA Write 2173 MB/s 54% CPU
64k: 16 tasks queuedepth=16
CPU Read: 36800 MB/s 1593% CPU DMA Read: 29100 MB/s 607% CPU
CPU Write 20900 MB/s 1589% CPU DMA Write: 23400 MB/s 585% CPU
2M: 1 task queuedepth=1
CPU Read: 6013 MB/s 99.3% CPU DMA Read: 7986 MB/s 59.3% CPU
CPU Write: 3579 MB/s 100% CPU DMA Write: 5211 MB/s 58.3% CPU
2M: 16 tasks queuedepth=16
CPU Read: 18100 MB/s 1588% CPU DMA Read: 21300 MB/s 180.9% CPU
CPU Write: 14100 MB/s 1594% CPU DMA Write: 20400 MB/s 446.9% CPU
Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
drivers/nvdimm/pmem.c | 214 +++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 204 insertions(+), 10 deletions(-)
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 519b949..8eeb646 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -32,6 +32,8 @@
#include <linux/dax.h>
#include <linux/nd.h>
#include <linux/blk-mq.h>
+#include <linux/dmaengine.h>
+#include <linux/dma-mapping.h>
#include "pmem.h"
#include "pfn.h"
#include "nd.h"
@@ -41,12 +43,24 @@ enum {
PMEM_Q_MQ = 1,
};
-static int queue_mode = PMEM_Q_BIO;
+static int queue_mode = PMEM_Q_MQ;
module_param(queue_mode, int, 0444);
-MODULE_PARM_DESC(queue_mode, "Pmem Queue Mode (0=BIO, 1=BLK-MQ)");
+MODULE_PARM_DESC(queue_mode, "Pmem Queue Mode (0=BIO, 1=BLK-MQ & DMA)");
+
+static int queue_depth = 128;
+module_param(queue_depth, int, 0444);
+MODULE_PARM_DESC(queue_depth, "I/O Queue Depth for multi queue mode");
+
+/* typically maps to number of DMA channels/devices per socket */
+static int q_per_node = 8;
+module_param(q_per_node, int, 0444);
+MODULE_PARM_DESC(q_per_node, "Hardware queues per node\n");
struct pmem_cmd {
struct request *rq;
+ struct dma_chan *chan;
+ int sg_nents;
+ struct scatterlist sg[];
};
static struct device *to_dev(struct pmem_device *pmem)
@@ -298,6 +312,159 @@ static void pmem_release_disk(void *__pmem)
put_disk(pmem->disk);
}
+static void nd_pmem_dma_callback(void *data,
+ const struct dmaengine_result *res)
+{
+ struct pmem_cmd *cmd = data;
+ struct request *req = cmd->rq;
+ struct request_queue *q = req->q;
+ struct pmem_device *pmem = q->queuedata;
+ struct nd_region *nd_region = to_region(pmem);
+ struct device *dev = to_dev(pmem);
+ int rc = 0;
+
+ if (res) {
+ enum dmaengine_tx_result dma_err = res->result;
+
+ switch (dma_err) {
+ case DMA_TRANS_READ_FAILED:
+ case DMA_TRANS_WRITE_FAILED:
+ case DMA_TRANS_ABORTED:
+ dev_dbg(dev, "bio failed\n");
+ rc = -ENXIO;
+ break;
+ case DMA_TRANS_NOERROR:
+ default:
+ break;
+ }
+ }
+
+ if (req->cmd_flags & REQ_FUA)
+ nvdimm_flush(nd_region);
+
+ blk_mq_end_request(cmd->rq, rc);
+}
+
+static int pmem_handle_cmd_dma(struct pmem_cmd *cmd, bool is_write)
+{
+ struct request *req = cmd->rq;
+ struct request_queue *q = req->q;
+ struct pmem_device *pmem = q->queuedata;
+ struct device *dev = to_dev(pmem);
+ phys_addr_t pmem_off = blk_rq_pos(req) * 512 + pmem->data_offset;
+ void *pmem_addr = pmem->virt_addr + pmem_off;
+ struct nd_region *nd_region = to_region(pmem);
+ size_t len;
+ struct dma_device *dma = cmd->chan->device;
+ struct dmaengine_unmap_data *unmap;
+ dma_cookie_t cookie;
+ struct dma_async_tx_descriptor *txd;
+ struct page *page;
+ unsigned int off;
+ int rc;
+ enum dma_data_direction dir;
+ dma_addr_t dma_addr;
+
+ if (req->cmd_flags & REQ_FLUSH)
+ nvdimm_flush(nd_region);
+
+ unmap = dmaengine_get_unmap_data(dma->dev, 2, GFP_NOWAIT);
+ if (!unmap) {
+ dev_dbg(dev, "failed to get dma unmap data\n");
+ rc = -ENOMEM;
+ goto err;
+ }
+
+ /*
+ * If reading from pmem, writing to scatterlist,
+ * and if writing to pmem, reading from scatterlist.
+ */
+ dir = is_write ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+ cmd->sg_nents = blk_rq_map_sg(req->q, req, cmd->sg);
+ if (cmd->sg_nents < 1) {
+ rc = -EINVAL;
+ goto err;
+ }
+
+ if (cmd->sg_nents > 128) {
+ rc = -ENOMEM;
+ dev_warn(dev, "Number of sg greater than allocated\n");
+ goto err;
+ }
+
+ rc = dma_map_sg(dma->dev, cmd->sg, cmd->sg_nents, dir);
+ if (rc < 1) {
+ rc = -ENXIO;
+ goto err;
+ }
+
+ len = blk_rq_payload_bytes(req);
+ page = virt_to_page(pmem_addr);
+ off = offset_in_page(pmem_addr);
+ dir = is_write ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
+ dma_addr = dma_map_page(dma->dev, page, off, len, dir);
+ if (dma_mapping_error(dma->dev, unmap->addr[0])) {
+ dev_dbg(dma->dev, "src DMA mapping error\n");
+ rc = -ENXIO;
+ goto err_unmap_sg;
+ }
+
+ unmap->len = len;
+
+ if (is_write) {
+ unmap->addr[0] = dma_addr;
+ dma_unmap_data_set_virt(unmap, cmd->sg, 1);
+ unmap->to_cnt = 1;
+ unmap->from_cnt = 0;
+ dma_unmap_data_sg_from_nents(unmap, 2) = cmd->sg_nents;
+ } else {
+ dma_unmap_data_set_virt(unmap, cmd->sg, 0);
+ unmap->addr[1] = dma_addr;
+ unmap->from_cnt = 1;
+ unmap->to_cnt = 0;
+ dma_unmap_data_sg_to_nents(unmap, 2) = cmd->sg_nents;
+ }
+
+ txd = dma->device_prep_dma_memcpy_sg(cmd->chan,
+ cmd->sg, cmd->sg_nents, dma_addr,
+ !is_write, DMA_PREP_INTERRUPT);
+ if (!txd) {
+ dev_dbg(dma->dev, "dma prep failed\n");
+ rc = -ENXIO;
+ goto err_unmap_buffer;
+ }
+
+ txd->callback_result = nd_pmem_dma_callback;
+ txd->callback_param = cmd;
+ dma_set_unmap(txd, unmap);
+ cookie = dmaengine_submit(txd);
+ if (dma_submit_error(cookie)) {
+ dev_dbg(dma->dev, "dma submit error\n");
+ rc = -ENXIO;
+ goto err_set_unmap;
+ }
+
+ dmaengine_unmap_put(unmap);
+ dma_async_issue_pending(cmd->chan);
+
+ return 0;
+
+err_set_unmap:
+ dmaengine_unmap_put(unmap);
+err_unmap_buffer:
+ dma_unmap_page(dev, dma_addr, len, dir);
+err_unmap_sg:
+ if (dir == DMA_TO_DEVICE)
+ dir = DMA_FROM_DEVICE;
+ else
+ dir = DMA_TO_DEVICE;
+ dma_unmap_sg(dev, cmd->sg, cmd->sg_nents, dir);
+ dmaengine_unmap_put(unmap);
+err:
+ blk_mq_end_request(cmd->rq, rc);
+ return rc;
+}
+
static int pmem_handle_cmd(struct pmem_cmd *cmd)
{
struct request *req = cmd->rq;
@@ -331,12 +498,18 @@ static blk_status_t pmem_queue_rq(struct blk_mq_hw_ctx *hctx,
const struct blk_mq_queue_data *bd)
{
struct pmem_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
+ struct request *req;
+ int rc;
- cmd->rq = bd->rq;
-
- blk_mq_start_request(bd->rq);
+ req = cmd->rq = bd->rq;
+ cmd->chan = dma_find_channel(DMA_MEMCPY_SG);
+ blk_mq_start_request(req);
- if (pmem_handle_cmd(cmd) < 0)
+ if (cmd->chan && bio_multiple_segments(req->bio))
+ rc = pmem_handle_cmd_dma(cmd, op_is_write(req_op(req)));
+ else
+ rc = pmem_handle_cmd(cmd);
+ if (rc < 0)
return BLK_STS_IOERR;
else
return BLK_STS_OK;
@@ -363,6 +536,7 @@ static int pmem_attach_disk(struct device *dev,
struct gendisk *disk;
void *addr;
int rc;
+ struct dma_chan *chan;
/* while nsio_rw_bytes is active, parse a pfn info block if present */
if (is_nd_pfn(dev)) {
@@ -396,11 +570,20 @@ static int pmem_attach_disk(struct device *dev,
}
if (queue_mode == PMEM_Q_MQ) {
+ chan = dma_find_channel(DMA_MEMCPY_SG);
+ if (!chan) {
+ queue_mode = PMEM_Q_BIO;
+ dev_warn(dev, "Forced back to PMEM_Q_BIO, no DMA\n");
+ }
+ }
+
+ if (queue_mode == PMEM_Q_MQ) {
pmem->tag_set.ops = &pmem_mq_ops;
- pmem->tag_set.nr_hw_queues = nr_online_nodes;
- pmem->tag_set.queue_depth = 64;
+ pmem->tag_set.nr_hw_queues = nr_online_nodes * q_per_node;
+ pmem->tag_set.queue_depth = queue_depth;
pmem->tag_set.numa_node = dev_to_node(dev);
- pmem->tag_set.cmd_size = sizeof(struct pmem_cmd);
+ pmem->tag_set.cmd_size = sizeof(struct pmem_cmd) +
+ sizeof(struct scatterlist) * 128;
pmem->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
pmem->tag_set.driver_data = pmem;
@@ -466,7 +649,11 @@ static int pmem_attach_disk(struct device *dev,
blk_queue_write_cache(pmem->q, wbc, fua);
blk_queue_physical_block_size(pmem->q, PAGE_SIZE);
blk_queue_logical_block_size(pmem->q, pmem_sector_size(ndns));
- blk_queue_max_hw_sectors(pmem->q, UINT_MAX);
+ if (queue_mode == PMEM_Q_MQ) {
+ blk_queue_max_hw_sectors(pmem->q, 0x200000);
+ blk_queue_max_segments(pmem->q, 128);
+ } else
+ blk_queue_max_hw_sectors(pmem->q, UINT_MAX);
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, pmem->q);
queue_flag_set_unlocked(QUEUE_FLAG_DAX, pmem->q);
pmem->q->queuedata = pmem;
@@ -628,15 +815,22 @@ static struct nd_device_driver nd_pmem_driver = {
static int __init pmem_init(void)
{
+ if (queue_mode == PMEM_Q_MQ)
+ dmaengine_get();
+
return nd_driver_register(&nd_pmem_driver);
}
module_init(pmem_init);
static void pmem_exit(void)
{
+ if (queue_mode == PMEM_Q_MQ)
+ dmaengine_put();
+
driver_unregister(&nd_pmem_driver.drv);
}
module_exit(pmem_exit);
+MODULE_SOFTDEP("pre: dmaengine");
MODULE_AUTHOR("Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>");
MODULE_LICENSE("GPL v2");
--
To unsubscribe from this list: send the line "unsubscribe dmaengine" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
