bitesize: switch to tracepoints (iovisor#2281)

bitesize: switch to tracepoints

man/man8/bitesize.8

@@ -6,8 +6,7 @@ bitesize \- Summarize block device I/O size as a histogram \- Linux eBPF/bcc.
 .SH DESCRIPTION
 Show I/O distribution for requested block sizes, by process name.
 
-This works by tracing block I/O kernel functions using dynamic
-tracing and prints a historgram of I/O size.
+This works by tracing block:block_rq_insert and prints a historgram of I/O size.
 
 Since this uses BPF, only the root user can use this tool.
 .SH REQUIREMENTS
@@ -29,7 +28,7 @@ distribution
 An ASCII bar chart to visualize the distribution (count column)
 
 .SH OVERHEAD
-This traces kernel block I/O functions to update a histgroam, which are
+This traces a block I/O tracepoint to update a histogram, which is
 asynchronously copied to user-space. This method is very efficient, and 
 the overhead for most storage I/O rates (< 10k IOPS) should be negligible. 
 If you have a higher IOPS storage environment, test and quantify the overhead 

tools/bitesize.py

@@ -11,6 +11,7 @@
 # Licensed under the Apache License, Version 2.0 (the "License")
 #
 # 05-Feb-2016 Allan McAleavy ran pep8 against file
+# 19-Mar-2019 Brendan Gregg Switched to use tracepoints.
 
 from bcc import BPF
 from time import sleep
@@ -24,47 +25,21 @@
  u64 slot;
 };
 
-struct val_t {
- char name[TASK_COMM_LEN];
-};
-
 BPF_HISTOGRAM(dist, struct proc_key_t);
-BPF_HASH(commbyreq, struct request *, struct val_t);
-
-int trace_pid_start(struct pt_regs *ctx, struct request *req)
-{
- struct val_t val = {};
 
- if (bpf_get_current_comm(&val.name, sizeof(val.name)) == 0) {
- commbyreq.update(&req, &val);
- }
- return 0;
-}
-
-int do_count(struct pt_regs *ctx, struct request *req)
+TRACEPOINT_PROBE(block, block_rq_insert)
 {
- struct val_t *valp;
-
- valp = commbyreq.lookup(&req);
- if (valp == 0) {
- return 0;
- }
-
- if (req->__data_len > 0) {
- struct proc_key_t key = {.slot = bpf_log2l(req->__data_len / 1024)};
- bpf_probe_read(&key.name, sizeof(key.name),valp->name);
- dist.increment(key);
- }
+ struct proc_key_t key = {.slot = bpf_log2l(args->bytes / 1024)};
+ bpf_probe_read(&key.name, sizeof(key.name), args->comm);
+ dist.increment(key);
  return 0;
 }
 """
 
 # load BPF program
 b = BPF(text=bpf_text)
-b.attach_kprobe(event="blk_account_io_start", fn_name="trace_pid_start")
-b.attach_kprobe(event="blk_account_io_completion", fn_name="do_count")
 
-print("Tracing... Hit Ctrl-C to end.")
+print("Tracing block I/O... Hit Ctrl-C to end.")
 
 # trace until Ctrl-C
 dist = b.get_table("dist")