target/rd: Add ramdisk bit for NULLIO operation

This patch adds a rd_nullio parameter that allows RAMDISK_MCP backends to function in NULLIO mode, where all se_cmd I/O is immediately completed in rd_execute_rw() without actually performing the SGL memory copy. This is useful for performance testing when the ramdisk SGL memory copy begins to eat lots of cycles during heavy small block workloads, so allow this bit to be enabled when necessary on a per rd_dev basis. Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

target/rd: Add ramdisk bit for NULLIO operation
This patch adds a rd_nullio parameter that allows RAMDISK_MCP backends to function in NULLIO mode, where all se_cmd I/O is immediately completed in rd_execute_rw() without actually performing the SGL memory copy. This is useful for performance testing when the ramdisk SGL memory copy begins to eat lots of cycles during heavy small block workloads, so allow this bit to be enabled when necessary on a per rd_dev basis. Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Nicholas Bellinger
1 parent 3eccfdb01d
Showing 2 changed files with 19 additions and 3 deletions Side-by-side Diff
drivers/target/target_core_rd.c
drivers/target/target_core_rd.h
@@ -291,6 +291,11 @@
 	u32 src_len;
 	u64 tmp;
  
+	if (dev->rd_flags & RDF_NULLIO) {
+		target_complete_cmd(cmd, SAM_STAT_GOOD);
+		return 0;
+	}
+
 	tmp = cmd->t_task_lba * se_dev->dev_attrib.block_size;
 	rd_offset = do_div(tmp, PAGE_SIZE);
 	rd_page = tmp;
  
@@ -373,11 +378,12 @@
 }
  
 enum {
-	Opt_rd_pages, Opt_err
+	Opt_rd_pages, Opt_rd_nullio, Opt_err
 };
  
 static match_table_t tokens = {
 	{Opt_rd_pages, "rd_pages=%d"},
+	{Opt_rd_nullio, "rd_nullio=%d"},
 	{Opt_err, NULL}
 };
  
@@ -408,6 +414,14 @@
 				" Count: %u\n", rd_dev->rd_page_count);
 			rd_dev->rd_flags |= RDF_HAS_PAGE_COUNT;
 			break;
+		case Opt_rd_nullio:
+			match_int(args, &arg);
+			if (arg != 1)
+				break;
+
+			pr_debug("RAMDISK: Setting NULLIO flag: %d\n", arg);
+			rd_dev->rd_flags |= RDF_NULLIO;
+			break;
 		default:
 			break;
 		}
@@ -424,8 +438,9 @@
 	ssize_t bl = sprintf(b, "TCM RamDisk ID: %u  RamDisk Makeup: rd_mcp\n",
 			rd_dev->rd_dev_id);
 	bl += sprintf(b + bl, "        PAGES/PAGE_SIZE: %u*%lu"
-			"  SG_table_count: %u\n", rd_dev->rd_page_count,
-			PAGE_SIZE, rd_dev->sg_table_count);
+			"  SG_table_count: %u  nullio: %d\n", rd_dev->rd_page_count,
+			PAGE_SIZE, rd_dev->sg_table_count,
+			!!(rd_dev->rd_flags & RDF_NULLIO));
 	return bl;
 }
  
@@ -22,6 +22,7 @@
 } ____cacheline_aligned;
  
 #define RDF_HAS_PAGE_COUNT	0x01
+#define RDF_NULLIO		0x02
  
 struct rd_dev {
 	struct se_device dev;
...	...	@@ -291,6 +291,11 @@
291	291	u32 src_len;
292	292	u64 tmp;
293	293
	294	+ if (dev->rd_flags & RDF_NULLIO) {
	295	+ target_complete_cmd(cmd, SAM_STAT_GOOD);
	296	+ return 0;
	297	+ }
	298	+
294	299	tmp = cmd->t_task_lba * se_dev->dev_attrib.block_size;
295	300	rd_offset = do_div(tmp, PAGE_SIZE);
296	301	rd_page = tmp;
297	302
...	...	@@ -373,11 +378,12 @@
373	378	}
374	379
375	380	enum {
376		- Opt_rd_pages, Opt_err
	381	+ Opt_rd_pages, Opt_rd_nullio, Opt_err
377	382	};
378	383
379	384	static match_table_t tokens = {
380	385	{Opt_rd_pages, "rd_pages=%d"},
	386	+ {Opt_rd_nullio, "rd_nullio=%d"},
381	387	{Opt_err, NULL}
382	388	};
383	389
...	...	@@ -408,6 +414,14 @@
408	414	" Count: %u\n", rd_dev->rd_page_count);
409	415	rd_dev->rd_flags \|= RDF_HAS_PAGE_COUNT;
410	416	break;
	417	+ case Opt_rd_nullio:
	418	+ match_int(args, &arg);
	419	+ if (arg != 1)
	420	+ break;
	421	+
	422	+ pr_debug("RAMDISK: Setting NULLIO flag: %d\n", arg);
	423	+ rd_dev->rd_flags \|= RDF_NULLIO;
	424	+ break;
411	425	default:
412	426	break;
413	427	}
...	...	@@ -424,8 +438,9 @@
424	438	ssize_t bl = sprintf(b, "TCM RamDisk ID: %u RamDisk Makeup: rd_mcp\n",
425	439	rd_dev->rd_dev_id);
426	440	bl += sprintf(b + bl, " PAGES/PAGE_SIZE: %u*%lu"
427		- " SG_table_count: %u\n", rd_dev->rd_page_count,
428		- PAGE_SIZE, rd_dev->sg_table_count);
	441	+ " SG_table_count: %u nullio: %d\n", rd_dev->rd_page_count,
	442	+ PAGE_SIZE, rd_dev->sg_table_count,
	443	+ !!(rd_dev->rd_flags & RDF_NULLIO));
429	444	return bl;
430	445	}
431	446
...	...	@@ -22,6 +22,7 @@
22	22	} ____cacheline_aligned;
23	23
24	24	#define RDF_HAS_PAGE_COUNT 0x01
	25	+#define RDF_NULLIO 0x02
25	26
26	27	struct rd_dev {
27	28	struct se_device dev;