[PATCH 2/2] mtd-utils: flash_speed: Measure read while write latency
Miquel Raynal
miquel.raynal at bootlin.com
Thu Nov 10 07:59:38 PST 2022
The Read While Write (RWW) feature allows to perform reads from the
flash array into cache while a program (from cache) or an erase
operation happens, provided that the two areas are located on different
banks.
The main benefit is the possible reduced latency when requesting to read
a page while a much longer operation is ongoing, like a write or an
erase.
We can try to compare the positive impact of such a feature by enhancing
the flash_speed test tool with the following test:
- Measure the time taken by an eraseblock write in parallel with an
eraseblock read.
- Measure when the read operation ends.
- Compare the two to get the latency saved with the RWW feature.
To be sure the mtd_write actually starts (and acquires the necessary
locks) before the mtd_read does, we use SCHED_FIFO at rather high
(arbitrary) priorities, respectively 42 and 41.
Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
---
tests/mtd-tests/Makemodule.am | 5 +-
tests/mtd-tests/flash_speed.c | 126 +++++++++++++++++++++++++++++++++-
2 files changed, 127 insertions(+), 4 deletions(-)
diff --git a/tests/mtd-tests/Makemodule.am b/tests/mtd-tests/Makemodule.am
index d849e3c..d02e9e4 100644
--- a/tests/mtd-tests/Makemodule.am
+++ b/tests/mtd-tests/Makemodule.am
@@ -7,9 +7,12 @@ flash_stress_LDADD = libmtd.a
flash_stress_CPPFLAGS = $(AM_CPPFLAGS)
flash_speed_SOURCES = tests/mtd-tests/flash_speed.c
-flash_speed_LDADD = libmtd.a
+flash_speed_LDADD = libmtd.a $(PTHREAD_LIBS)
flash_speed_CPPFLAGS = $(AM_CPPFLAGS)
+flash_speed_LDADD += $(PTHREAD_CFLAGS)
+flash_speed_CPPFLAGS += $(PTHREAD_CFLAGS)
+
nandbiterrs_SOURCES = tests/mtd-tests/nandbiterrs.c
nandbiterrs_LDADD = libmtd.a
nandbiterrs_CPPFLAGS = $(AM_CPPFLAGS)
diff --git a/tests/mtd-tests/flash_speed.c b/tests/mtd-tests/flash_speed.c
index 035768b..0f82047 100644
--- a/tests/mtd-tests/flash_speed.c
+++ b/tests/mtd-tests/flash_speed.c
@@ -33,6 +33,7 @@
#include <stdlib.h>
#include <libmtd.h>
#include <getopt.h>
+#include <pthread.h>
#include <stdio.h>
#include <fcntl.h>
#include <time.h>
@@ -46,7 +47,7 @@ static const char *mtddev;
static libmtd_t mtd_desc;
static int fd;
-static int peb=-1, count=-1, skip=-1, flags=0;
+static int peb=-1, count=-1, skip=-1, flags=0, speb=-1;
static struct timespec start, finish;
static int pgsize, pgcnt;
static int goodebcnt;
@@ -57,6 +58,7 @@ static const struct option options[] = {
{ "peb", required_argument, NULL, 'b' },
{ "count", required_argument, NULL, 'c' },
{ "skip", required_argument, NULL, 's' },
+ { "sec-peb", required_argument, NULL, 'k' },
{ NULL, 0, NULL, 0 },
};
@@ -69,7 +71,8 @@ static NORETURN void usage(int status)
" -b, --peb <num> Start from this physical erase block\n"
" -c, --count <num> Number of erase blocks to use (default: all)\n"
" -s, --skip <num> Number of blocks to skip\n"
- " -d, --destructive Run destructive (erase and write speed) tests\n",
+ " -d, --destructive Run destructive (erase and write speed) tests\n"
+ " -k, --sec-peb <num> Start of secondary block to measure RWW latency (requires -d)\n",
status==EXIT_SUCCESS ? stdout : stderr);
exit(status);
}
@@ -93,7 +96,7 @@ static void process_options(int argc, char **argv)
int c;
while (1) {
- c = getopt_long(argc, argv, "hb:c:s:d", options, NULL);
+ c = getopt_long(argc, argv, "hb:c:s:dk:", options, NULL);
if (c == -1)
break;
@@ -126,6 +129,13 @@ static void process_options(int argc, char **argv)
goto failmulti;
flags |= DESTRUCTIVE;
break;
+ case 'k':
+ if (speb >= 0)
+ goto failmulti;
+ speb = read_num(c, optarg);
+ if (speb < 0)
+ goto failarg;
+ break;
default:
exit(EXIT_FAILURE);
}
@@ -144,11 +154,15 @@ static void process_options(int argc, char **argv)
skip = 0;
if (count < 0)
count = 1;
+ if (speb >= 0 && !(flags & DESTRUCTIVE))
+ goto faildestr;
return;
failmulti:
errmsg_die("'-%c' specified more than once!\n", c);
failarg:
errmsg_die("Invalid argument for '-%c'!\n", c);
+faildestr:
+ errmsg_die("'-k' specified, -d is missing!\n");
}
static int write_eraseblock(int ebnum)
@@ -320,6 +334,32 @@ static int erase_good_eraseblocks(unsigned int eb, int ebcnt, int ebskip)
return err;
}
+struct thread_arg {
+ int (*op)(int peb);
+ int peb;
+ struct timespec start;
+ struct timespec finish;
+};
+
+static void *op_thread(void *ptr)
+{
+ struct thread_arg *args = ptr;
+ unsigned long err = 0;
+ int i;
+
+ start_timing(&args->start);
+ for (i = 0; i < count; ++i) {
+ if (bbt[i])
+ continue;
+ err = args->op(args->peb + i * (skip + 1));
+ if (err)
+ break;
+ }
+ stop_timing(&args->finish);
+
+ return (void *)err;
+}
+
#define TIME_OP_PER_PEB( op )\
start_timing(&start);\
for (i = 0; i < count; ++i) {\
@@ -470,6 +510,86 @@ int main(int argc, char **argv)
}
}
+ /* Write a page and immediately after try to read another page. Report
+ * the latency difference when performed on different banks (NOR only).
+ */
+ if (speb >= 0 && mtd.subpage_size == 1) {
+ long duration_w, duration_r, rww_duration_w, rww_latency_end;
+ long rww_duration_rnw, rww_duration_r_end;
+ bool rww_r_end_first;
+ struct thread_arg write_args_peb = {
+ .op = write_eraseblock,
+ .peb = peb,
+ };
+ struct thread_arg read_args_speb = {
+ .op = read_eraseblock,
+ .peb = speb,
+ };
+ struct sched_param param_write, param_read;
+ pthread_attr_t attr_write, attr_read;
+ pthread_t write_thread, read_thread;
+ void *retval;
+
+ puts("testing read while write latency");
+
+ /* Change scheduling priorities so that the write thread gets
+ *scheduled more aggressively than the read thread.
+ */
+ pthread_attr_init(&attr_write);
+ pthread_attr_setinheritsched(&attr_write, PTHREAD_EXPLICIT_SCHED);
+ pthread_attr_setschedpolicy(&attr_write, SCHED_FIFO);
+ param_write.sched_priority = 42;
+ pthread_attr_setschedparam(&attr_write, ¶m_write);
+
+ pthread_attr_init(&attr_read);
+ pthread_attr_setinheritsched(&attr_read, PTHREAD_EXPLICIT_SCHED);
+ pthread_attr_setschedpolicy(&attr_read, SCHED_FIFO);
+ param_read.sched_priority = 41;
+ pthread_attr_setschedparam(&attr_read, ¶m_read);
+
+ err = pthread_create(&write_thread, &attr_write,
+ (void *)op_thread, &write_args_peb);
+ if (err) {
+ errmsg("parallel write pthread create failed");
+ goto out;
+ }
+
+ err = pthread_create(&read_thread, &attr_read,
+ (void *)op_thread, &read_args_speb);
+ if (err) {
+ errmsg("parallel read pthread create failed");
+ goto out;
+ }
+
+ pthread_join(read_thread, &retval);
+ if ((long)retval) {
+ errmsg("parallel read pthread failed");
+ goto out;
+ }
+
+ pthread_join(write_thread, &retval);
+ if ((long)retval) {
+ errmsg("parallel write pthread failed");
+ goto out;
+ }
+
+ rww_duration_w = calc_duration(&write_args_peb.start,
+ &write_args_peb.finish);
+ rww_latency_end = calc_duration(&write_args_peb.finish,
+ &read_args_speb.finish);
+ rww_r_end_first = rww_latency_end < 0;
+ if (rww_r_end_first)
+ rww_duration_rnw = rww_duration_w;
+ else
+ rww_duration_rnw = calc_duration(&write_args_peb.start,
+ &read_args_speb.finish);
+
+ rww_duration_r_end = calc_duration(&write_args_peb.start,
+ &read_args_speb.finish);
+ printf("read while write took %ldms, read ended after %ldms\n",
+ rww_duration_rnw, rww_duration_r_end);
+ }
+
puts("finished");
status = EXIT_SUCCESS;
out:
--
2.34.1
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