[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint contr
From: |
Stefan Hajnoczi |
Subject: |
Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event) |
Date: |
Tue, 19 Oct 2010 15:44:07 +0100 |
User-agent: |
Mutt/1.5.20 (2009-06-14) |
On Tue, Oct 19, 2010 at 03:29:51PM +0100, Richard W.M. Jones wrote:
> On Tue, Oct 19, 2010 at 03:59:36PM +0200, Jan Kiszka wrote:
> > Once we have "-trace events=...", defining the list of active
> > tracepoints before starting qemu will be trivial (e.g. via a config
> > file). Of course, this requires that all tracepoints are built-in...
>
> Sorry that I've not been following this very closely, but does this
> sort of thing allow tracing reads and writes to block devices? Am I
> right in thinking that if a tracepoint existed in the right place, one
> could get a log file from that which could be post-processed in
> another tool?
>
> cf:
> http://rwmj.wordpress.com/2010/10/05/visualizing-reads-writes-and-alignment/#content
Definitely, here is the commit that added bdrv_aio_writev/bdrv_aio_readv
tracing. bdrv_aio_multiwrite has been traced for a while.
http://patchwork.ozlabs.org/patch/66843/
As an example, I use the following script to find all write requests
that touch a given region. This is very useful for debugging image
corruptions given a trace file:
The usage is:
find_overlapping_io.py <bs> <sector_num> <nb_sectors>
where bs is the block driver state pointer, sector_num is the starting
sector address, and nb_sectors is the number of sectors.
#!/usr/bin/env python
import sys
def trace_filter(fobj, event, keys):
for line in fobj:
fields = line.strip().split()
if fields[0] != event:
continue
attrs = dict([(k, v) for k, v in (x.split('=') for x in fields[2:])])
match = True
for k, v in keys.iteritems():
if k not in attrs:
match = False
break
if attrs[k] != v:
match = False
break
if match:
yield attrs
def intersection(a_sector_num, a_nb_sectors, b_sector_num, b_nb_sectors):
return not (a_sector_num + a_nb_sectors <= b_sector_num or \
b_sector_num + b_nb_sectors <= a_sector_num)
bs, sector_num, nb_sectors = sys.argv[1:]
sector_num = int(sector_num, 0)
nb_sectors = int(nb_sectors, 0)
for req in trace_filter(sys.stdin, 'bdrv_aio_writev', {'bs': bs}):
if intersection(sector_num, nb_sectors, int(req['sector_num'], 0),
int(req['nb_sectors'], 0)):
print req
Stefan
- [Qemu-devel] Re: Static tracepoint control via trace-event, (continued)
- Re: [Qemu-devel] Static tracepoint control via trace-event, Daniel P. Berrange, 2010/10/19
- Re: [Qemu-devel] Static tracepoint control via trace-event, Stefan Hajnoczi, 2010/10/19
- Re: [Qemu-devel] Static tracepoint control via trace-event, Jan Kiszka, 2010/10/19
- Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Richard W.M. Jones, 2010/10/19
- [Qemu-devel] Re: Tracing block devices, Jan Kiszka, 2010/10/19
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event),
Stefan Hajnoczi <=
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Christoph Hellwig, 2010/10/21
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Richard W.M. Jones, 2010/10/21
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Stefan Hajnoczi, 2010/10/21
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Daniel P. Berrange, 2010/10/21