1. In the Storage-Backup environment of HyperCluster, includes one storage array near
to the host and one remote storage array, and the two storage arrays have the same hardware.
The same LUN is writed or readed by the two storage arrays. However, usually, the average
latency of the paths of the remote storage array is much higher than the near storage array's.
Apparently, the prioritizer can be a good automatic solution. And the current selectors don't
solve it, IOs will send to the paths of the remote storage array, IOPS will be influenced unavoidably.
2. In the environment of single storage array, the prioritizer can automatically separate the paths
who's latency is much higher, IOs will not send to this paths. But the current selectors don't solve
this problem, IOPS will be influenced unavoidably.
The value of "MIN_IO_NUM" is set 2 from 10, the patch v2 as follows:
---
Subject: [PATCH] libmultipath/prioritizers: Prioritizer for device mapper multipath, where the corresponding priority
values of specific paths are provided by a latency algorithm. And the latency algorithm is dependent on the following
arguments(latency_interval and io_num). The principle of the algorithm is illustrated as follows:
1. By sending a certain number "cons_num" of read IOs to the current path continuously, the IOs' average latency can be calculated.
2. According to the average latency of each path and the weight value "latency_interval", the priority "rc" of each path can be provided.
latency_interval latency_interval latency_interval latency_interval
|------------------|------------------|------------------|...|------------------|
| priority rank 1 | priority rank 2 | priority rank 3 |...| priority rank x |
|------------------|------------------|------------------|...|------------------|
Priority Rank Partitioning
---
libmultipath/prioritizers/Makefile | 6 +-
libmultipath/prioritizers/path_latency.c | 271 +++++++++++++++++++++++++++++++
multipath/multipath.conf.5 | 18 ++
libmultipath/prio.h | 1 +
4 files changed, 295 insertions(+), 1 deletion(-)
create mode 100644 libmultipath/prioritizers/path_latency.c
diff --git a/libmultipath/prioritizers/Makefile b/libmultipath/prioritizers/Makefile
index 36b42e4..d2f20f6 100644
--- a/libmultipath/prioritizers/Makefile
+++ b/libmultipath/prioritizers/Makefile
@@ -18,13 +18,17 @@ LIBS = \
libpriorandom.so \
libpriordac.so \
libprioweightedpath.so \
- libpriosysfs.so
+ libpriopath_latency.so \
+ libpriosysfs.so
all: $(LIBS)
libprioalua.so: alua.o alua_rtpg.o
$(CC) $(LDFLAGS) $(SHARED_FLAGS) -o $@ $^
+libpriopath_latency.so: path_latency.o ../checkers/libsg.o
+ $(CC) $(LDFLAGS) $(SHARED_FLAGS) -o $@ $^ -lm
+
libprio%.so: %.o
$(CC) $(LDFLAGS) $(SHARED_FLAGS) -o $@ $^
diff --git a/libmultipath/prioritizers/path_latency.c b/libmultipath/prioritizers/path_latency.c
new file mode 100644
index 0000000..a666b6c
--- /dev/null
+++ b/libmultipath/prioritizers/path_latency.c
@@ -0,0 +1,271 @@
+/*
+ * (C) Copyright HUAWEI Technology Corp. 2017, 2021 All Rights Reserved.
+ *
+ * main.c
+ *
+ * Prioritizer for device mapper multipath, where the corresponding priority
+ * values of specific paths are provided by a latency algorithm. And the
+ * latency algorithm is dependent on arguments.
+ *
+ * The principle of the algorithm as follows:
+ * 1. By sending a certain number "io_num" of read IOs to the current path
+ * continuously, the IOs' average latency can be calculated.
+ * 2. According to the average latency of each path and the weight value
+ * "latency_interval", the priority "rc" of each path can be provided.
+ *
+ * Author(s): Yang Feng <philip.yang@xxxxxxxxxx>
+ * Zou Ming <zouming.zouming@xxxxxxxxxx>
+ *
+ * This file is released under the GPL.
+ */
+#include <stdio.h>
+#include <math.h>
+#include <ctype.h>
+#include <time.h>
+
+#include "debug.h"
+#include "prio.h"
+#include "structs.h"
+#include "../checkers/libsg.h"
+
+#define THRES_USEC_VALUE 120000000LL /*unit: us, =120s*/
+
+#define MAX_IO_NUM 200
+#define MIN_IO_NUM 2
+
+#define MAX_LATENCY_INTERVAL 60 /*unit: s*/
+#define MIN_LATENCY_INTERVAL 1 /*unit: us, or ms, or s*/
+
+#define DEFAULT_PRIORITY 0
+
+#define MAX_CHAR_SIZE 30
+
+#define CHAR_USEC "us"
+#define CHAR_MSEC "ms"
+#define CHAR_SEC "s"
+
+enum interval_type {
+ INTERVAL_USEC,
+ INTERVAL_MSEC,
+ INTERVAL_SEC,
+ INTERVAL_INVALID
+};
+
+/* interval_unit_str and interval_unit_type keep the same assignment sequence */
+static const char *interval_unit_str[MAX_CHAR_SIZE] = {
+ CHAR_USEC, CHAR_MSEC, CHAR_SEC
+};
+static const int interval_unit_type[] = {
+ INTERVAL_USEC, INTERVAL_MSEC, INTERVAL_SEC
+};
+
+#define USEC_PER_SEC 1000000LL
+#define USEC_PER_MSEC 1000LL
+#define USEC_PER_USEC 1LL
+
+static const int conversion_ratio[] = {
+ [INTERVAL_USEC] = USEC_PER_USEC,
+ [INTERVAL_MSEC] = USEC_PER_MSEC,
+ [INTERVAL_SEC] = USEC_PER_SEC,
+ [INTERVAL_INVALID] = 0
+};
+
+static long long path_latency[MAX_IO_NUM];
+
+static inline long long timeval_to_us(const struct timespec *tv)
+{
+ return ((long long) tv->tv_sec * USEC_PER_SEC) + (tv->tv_nsec >> 10);
+}
+
+static int do_readsector0(int fd, unsigned int timeout)
+{
+ unsigned char buf[4096];
+ unsigned char sbuf[SENSE_BUFF_LEN];
+ int ret;
+
+ ret = sg_read(fd, &buf[0], 4096, &sbuf[0],
+ SENSE_BUFF_LEN, timeout);
+
+ return ret;
+}
+
+int check_args_valid(int io_num, long long latency_interval, int type)
+{
+ if ((io_num < MIN_IO_NUM) || (io_num > MAX_IO_NUM))
+ {
+ condlog(0, "args io_num is more than the valid values range");
+ return 0;
+ }
+
+ /* s:[1, 60], ms:[1, 60000], us:[1, 60000000] */
+ if ((latency_interval < MIN_LATENCY_INTERVAL) || (latency_interval > (MAX_LATENCY_INTERVAL * USEC_PER_SEC / conversion_ratio[type])))
+ {
+ condlog(0, "args latency_interval is more than the valid values range");
+ return 0;
+ }
+
+ return 1;
+}
+
+static int get_interval_type(char *type)
+{
+ int index;
+
+ for (index = 0; index < sizeof(interval_unit_str)/MAX_CHAR_SIZE; index++)
+ {
+ if (strcmp(type, interval_unit_str[index]) == 0)
+ {
+ return interval_unit_type[index];
+ }
+ }
+
+ return INTERVAL_INVALID;
+}
+
+long long get_conversion_ratio(int type)
+{
+ return conversion_ratio[type];
+}
+
+/* In multipath.conf, args form: io_num|latency_interval. For example,
+* args is "20|10ms", this function can get 20, 10.
+*/
+static int get_interval_and_ionum(char *args,
+ int *ionum,
+ long long *interval)
+{
+ char source[MAX_CHAR_SIZE];
+ char vertica = '|';
+ char *endstrbefore = NULL;
+ char *endstrafter = NULL;
+ int type;
+ unsigned int size = strlen(args);
+ long long ratio;
+
+ if ((args == NULL) || (ionum == NULL) || (interval == NULL))
+ {
+ condlog(0, "args string is NULL");
+ return 0;
+ }
+
+ if ((size < 1) || (size > MAX_CHAR_SIZE-1))
+ {
+ condlog(0, "args string's size is too long");
+ return 0;
+ }
+
+ memcpy(source, args, size+1);
+
+ if (!isdigit(source[0]))
+ {
+ condlog(0, "args io_num string's first char is not digit");
+ return 0;
+ }
+
+ *ionum = (int)strtoul(source, &endstrbefore, 10);
+ if (endstrbefore[0] != vertica)
+ {
+ condlog(0, "segmentation char is invalid");
+ return 0;
+ }
+
+ if (!isdigit(endstrbefore[1]))
+ {
+ condlog(0, "args latency_interval string's first char is not digit");
+ return 0;
+ }
+
+ *interval = (long long)strtol(&endstrbefore[1], &endstrafter, 10);
+ type = get_interval_type(endstrafter);
+ if (type == INTERVAL_INVALID)
+ {
+ condlog(0, "args latency_interval type is invalid");
+ return 0;
+ }
+
+ if (check_args_valid(*ionum, *interval, type) == 0)
+ {
+ return 0;
+ }
+
+ ratio = get_conversion_ratio(type);
+ *interval *= (long long)ratio;
+
+ return 1;
+}
+
+long long calc_standard_deviation(long long *path_latency, int size, long long avglatency)
+{
+ int index;
+ long long total = 0;
+
+ for (index = 0; index < size; index++)
+ {
+ total += (path_latency[index] - avglatency) * (path_latency[index] - avglatency);
+ }
+
+ total /= (size-1);
+
+ return (long long)sqrt((double)total);
+}
+
+int getprio (struct path *pp, char *args, unsigned int timeout)
+{
+ int rc, temp;
+ int index = 0;
+ int io_num;
+ long long latency_interval;
+ long long avglatency;
+ long long standard_deviation;
+ long long toldelay = 0;
+ long long before, after;
+ struct timespec tv;
+
+ if (pp->fd < 0)
+ return -1;
+
+ if (get_interval_and_ionum(args, &io_num, &latency_interval) == 0)
+ {
+ condlog(0, "%s: get path_latency args fail", pp->dev);
+ return DEFAULT_PRIORITY;
+ }
+
+ memset(path_latency, 0, sizeof(path_latency));
+
+ temp = io_num;
+ while (temp-- > 0)
+ {
+ (void)clock_gettime(CLOCK_MONOTONIC, &tv);
+ before = timeval_to_us(&tv);
+
+ if (do_readsector0(pp->fd, timeout) == 2)
+ {
+ condlog(0, "%s: path down", pp->dev);
+ return -1;
+ }
+
+ (void)clock_gettime(CLOCK_MONOTONIC, &tv);
+ after = timeval_to_us(&tv);
+
+ path_latency[index] = after - before;
+ toldelay += path_latency[index++];
+ }
+
+ avglatency = toldelay/(long long)io_num;
+ condlog(4, "%s: average latency is (%lld)", pp->dev, avglatency);
+
+ if (avglatency > THRES_USEC_VALUE)
+ {
+ condlog(0, "%s: average latency (%lld) is more than thresold", pp->dev, avglatency);
+ return DEFAULT_PRIORITY;
+ }
+
+ /* warn the user if the latency_interval set is smaller than (2 * standard deviation), or equal */
+ standard_deviation = calc_standard_deviation(path_latency, index, avglatency);
+ if (latency_interval <= (2 * standard_deviation))
+ condlog(3, "%s: args latency_interval set is smaller than 2 * standard deviation (%lld us), or equal",
+ pp->dev, standard_deviation);
+
+ rc = (int)(THRES_USEC_VALUE - (avglatency/(long long)latency_interval));
+ return rc;
+}
diff --git a/multipath/multipath.conf.5 b/multipath/multipath.conf.5
index 5939688..3dd0d77 100644
--- a/multipath/multipath.conf.5
+++ b/multipath/multipath.conf.5
@@ -293,6 +293,10 @@ Generate a random priority between 1 and 10.
Generate the path priority based on the regular expression and the
priority provided as argument. Requires prio_args keyword.
.TP
+.I path_latency
+Generate the path priority based on a latency algorithm.
+Requires prio_args keyword.
+.TP
.I datacore
.\" XXX
???. Requires prio_args keyword.
@@ -333,6 +337,20 @@ these values can be looked up through sysfs or by running \fImultipathd show pat
"%N:%R:%n:%r"\fR. For example: 0x200100e08ba0aea0:0x210100e08ba0aea0:.*:.* , .*:.*:iqn.2009-10.com.redhat.msp.lab.ask-06:.*
.RE
.TP 12
+.I path_latency
+Needs a value of the form
+\fI"<latency_interval>|<io_num>"\fR
+.RS
+.TP 8
+.I latency_interval
+The interval values of average latency between two different neighbour ranks of path priority, used to partition different priority ranks.
+Form: XXs, or XXXus, or XXXms. Unit: Second, or Microsecond, or Millisecond. Valid Values: Integer, s [1, 60], ms [1, 60000], us [1, 60000000],
+For example: If latency_interval=10ms, the paths will be grouped in priority groups with path latency 0-10ms, 10-20ms, 20-30ms, etc..
+.TP
+.I io_num
+The number of read IOs sent to the current path continuously, used to calculate the average path latency. Valid Values: Integer, [2, 200].
+.RE
+.TP 12
.I alua
If \fIexclusive_pref_bit\fR is set, paths with the \fIpreferred path\fR bit
set will always be in their own path group.
diff --git a/libmultipath/prio.h b/libmultipath/prio.h
index 0193c52..c97fe39 100644
--- a/libmultipath/prio.h
+++ b/libmultipath/prio.h
@@ -29,6 +29,7 @@ struct path;
#define PRIO_RDAC "rdac"
#define PRIO_WEIGHTED_PATH "weightedpath"
#define PRIO_SYSFS "sysfs"
+#define PRIO_PATH_LATENCY "path_latency"
/*
* Value used to mark the fact prio was not defined
--
--
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