tools/biosnoop: Add support for displaying block I/O pattern

man/man8/biosnoop.8

@@ -2,7 +2,7 @@
 .SH NAME
 biosnoop \- Trace block device I/O and print details incl. issuing PID.
 .SH SYNOPSIS
-.B biosnoop [\-h] [\-Q] [\-d DISK]
+.B biosnoop [\-h] [\-Q] [\-d DISK] [\-P]
 .SH DESCRIPTION
 This tools traces block device I/O (disk I/O), and prints a one-line summary
 for each I/O showing various details. These include the latency from the time of
@@ -32,6 +32,9 @@ Include a column showing the time spent queued in the OS.
 .TP
 \-d DISK
 Trace this disk only.
+.TP
+\-P
+Display block I/O pattern (sequential or random).
 .SH EXAMPLES
 .TP
 Trace all block device I/O and print a summary line per I/O:

tools/biosnoop.py

@@ -13,6 +13,7 @@
 # 16-Sep-2015   Brendan Gregg   Created this.
 # 11-Feb-2016   Allan McAleavy  updated for BPF_PERF_OUTPUT
 # 21-Jun-2022   Rocky Xing      Added disk filter support.
+# 13-Oct-2022   Rocky Xing      Added support for displaying block I/O pattern.
 
 from __future__ import print_function
 from bcc import BPF
@@ -24,6 +25,7 @@
     ./biosnoop           # trace all block I/O
     ./biosnoop -Q        # include OS queued time
     ./biosnoop -d sdc    # trace sdc only
+    ./biosnoop -P        # display block I/O pattern
 """
 parser = argparse.ArgumentParser(
     description="Trace block I/O",
@@ -32,17 +34,24 @@
 parser.add_argument("-Q", "--queue", action="store_true",
     help="include OS queued time")
 parser.add_argument("-d", "--disk", type=str,
-    help="Trace this disk only")
+    help="trace this disk only")
+parser.add_argument("-P", "--pattern", action="store_true",
+    help="display block I/O pattern (sequential or random)")
 parser.add_argument("--ebpf", action="store_true",
     help=argparse.SUPPRESS)
 args = parser.parse_args()
 debug = 0
 
 # define BPF program
-bpf_text="""
+bpf_text = """
 #include <uapi/linux/ptrace.h>
 #include <linux/blk-mq.h>
+"""
+
+if args.pattern:
+    bpf_text += "#define INCLUDE_PATTERN\n"
 
+bpf_text += """
 // for saving the timestamp and __data_len of each request
 struct start_req_t {
     u64 ts;
@@ -55,18 +64,38 @@
     char name[TASK_COMM_LEN];
 };
 
+#ifdef INCLUDE_PATTERN
+struct sector_key_t {
+    u32 dev_major;
+    u32 dev_minor;
+};
+
+enum bio_pattern {
+    UNKNOWN,
+    SEQUENTIAL,
+    RANDOM,
+};
+#endif
+
 struct data_t {
     u32 pid;
     u64 rwflag;
     u64 delta;
     u64 qdelta;
     u64 sector;
     u64 len;
+#ifdef INCLUDE_PATTERN
+    enum bio_pattern pattern;
+#endif
     u64 ts;
     char disk_name[DISK_NAME_LEN];
     char name[TASK_COMM_LEN];
 };
 
+#ifdef INCLUDE_PATTERN
+BPF_HASH(last_sectors, struct sector_key_t, u64);
+#endif
+
 BPF_HASH(start, struct request *, struct start_req_t);
 BPF_HASH(infobyreq, struct request *, struct val_t);
 BPF_PERF_OUTPUT(events);
@@ -108,6 +137,7 @@
     struct start_req_t *startp;
     struct val_t *valp;
     struct data_t data = {};
+    struct gendisk *rq_disk;
     u64 ts;
 
     // fetch timestamp and calculate delta
@@ -117,12 +147,13 @@
         return 0;
     }
     ts = bpf_ktime_get_ns();
+    rq_disk = req->__RQ_DISK__;
     data.delta = ts - startp->ts;
     data.ts = ts / 1000;
     data.qdelta = 0;
+    data.len = startp->data_len;
 
     valp = infobyreq.lookup(&req);
-    data.len = startp->data_len;
     if (valp == 0) {
         data.name[0] = '?';
         data.name[1] = 0;
@@ -133,11 +164,29 @@
         data.pid = valp->pid;
         data.sector = req->__sector;
         bpf_probe_read_kernel(&data.name, sizeof(data.name), valp->name);
-        struct gendisk *rq_disk = req->__RQ_DISK__;
         bpf_probe_read_kernel(&data.disk_name, sizeof(data.disk_name),
                        rq_disk->disk_name);
     }
 
+#ifdef INCLUDE_PATTERN
+    data.pattern = UNKNOWN;
+
+    u64 *sector, last_sector;
+
+    struct sector_key_t sector_key = {
+        .dev_major = rq_disk->major,
+        .dev_minor = rq_disk->first_minor
+    };
+
+    sector = last_sectors.lookup(&sector_key);
+    if (sector != 0) {
+        data.pattern = req->__sector == *sector ? SEQUENTIAL : RANDOM;
+    }
+
+    last_sector = req->__sector + data.len / 512;
+    last_sectors.update(&sector_key, &last_sector);
+#endif
+
 /*
  * The following deals with a kernel version change (in mainline 4.7, although
  * it may be backported to earlier kernels) with how block request write flags
@@ -218,15 +267,21 @@
 # header
 print("%-11s %-14s %-7s %-9s %-1s %-10s %-7s" % ("TIME(s)", "COMM", "PID",
     "DISK", "T", "SECTOR", "BYTES"), end="")
+if args.pattern:
+    print("%-1s " % ("P"), end="")
 if args.queue:
     print("%7s " % ("QUE(ms)"), end="")
 print("%7s" % "LAT(ms)")
 
 rwflg = ""
+pattern = ""
 start_ts = 0
 prev_ts = 0
 delta = 0
 
+P_SEQUENTIAL = 1
+P_RANDOM = 2
+
 # process event
 def print_event(cpu, data, size):
     event = b["events"].event(data)
@@ -249,6 +304,14 @@ def print_event(cpu, data, size):
     print("%-11.6f %-14.14s %-7s %-9s %-1s %-10s %-7s" % (
         delta / 1000000, event.name.decode('utf-8', 'replace'), event.pid,
         disk_name, rwflg, event.sector, event.len), end="")
+    if args.pattern:
+        if event.pattern == P_SEQUENTIAL:
+            pattern = "S"
+        elif event.pattern == P_RANDOM:
+            pattern = "R"
+        else:
+            pattern = "?"
+        print("%-1s " % pattern, end="")
     if args.queue:
         print("%7.2f " % (float(event.qdelta) / 1000000), end="")
     print("%7.2f" % (float(event.delta) / 1000000))

tools/biosnoop_example.txt

@@ -64,16 +64,18 @@ TIME(s)     COMM           PID    DISK    T SECTOR     BYTES  QUE(ms) LAT(ms)
 
 USAGE message:
 
-usage: biosnoop.py [-h] [-Q] [-d DISK]
+usage: biosnoop.py [-h] [-Q] [-d DISK] [-P]
 
 Trace block I/O
 
 optional arguments:
   -h, --help            show this help message and exit
   -Q, --queue           include OS queued time
-  -d DISK, --disk DISK  Trace this disk only
+  -d DISK, --disk DISK  trace this disk only
+  -P, --pattern         display block I/O pattern (sequential or random)
 
 examples:
     ./biosnoop           # trace all block I/O
     ./biosnoop -Q        # include OS queued time
     ./biosnoop -d sdc    # trace sdc only
+    ./biosnoop -P        # display block I/O pattern