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bitesize: switch to tracepoints #2281

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Mar 20, 2019
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bitesize: switch to tracepoints #2281

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bitesize: switch to tracepoints
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@brendangregg
brendangregg committed Mar 20, 2019
commit f7148cc7c0d99f2bc76067b516af1ae5040c6550
5 changes: 2 additions & 3 deletions man/man8/bitesize.8
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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
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37 changes: 6 additions & 31 deletions tools/bitesize.py
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Expand Up @@ -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
Expand All @@ -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")
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