Re: PATCH 1/3] blktrace: support per-partition tracing

[Ingo Molnar <mingo@elte.hu>]

* Li Zefan <lizf@cn.fujitsu.com> wrote:

> Ingo Molnar wrote:
> > * Li Zefan <lizf@cn.fujitsu.com> wrote:
> > 
> >> From: Shawn Du <duyuyang@gmail.com>
> >>
> >> Though one can specify '-d /dev/sda1' when using blktrace, it 
> >> still traces the whole sda.
> >>
> >> To support per-partition tracing, when we start tracing, we 
> >> initialize bt->start_lba and bt->end_lba to the start and end 
> >> sector of that partition.
> >>
> >> Note some actions are per device, thus we don't filter 0-sector 
> >> events.
> >>
> >> The original patch and discussion can be found here:
> >> 	http://marc.info/?l=linux-btrace&m\x122949374214540&w=2
> >>
> >> Signed-off-by: Shawn Du <duyuyang@gmail.com>
> >> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> > 
> > Thanks - beyond the small detail i mailed about a few minutes ago 
> > the series looks good: i'll queue this up in tracing/blktrace unless 
> > Jens has second thoughts.
> > 
> > Lets note that this approach still has the (long existing) 
> > limitation that only one device can be block-traced at a time.
> > 
> 
> No, both userspace blktrace and ftrace-plugin trace can trace
> more than one device at a time.
> 
>  # btrace /dev/sda /dev/dm-0
> 
> or
> 
>  # echo 1 > /sys/block/sda/trace/enable
>  # echo 1 > /sys/block/dm-0/trace/enable

When they are independent - but not multiple partitions at a time:

 [root@aldebaran ~]# echo 1 > /sys/block/sda/sda1/trace/enable 
 [root@aldebaran ~]# echo 1 > /sys/block/sda/sda2/trace/enable 
 -bash: echo: write error: Device or resource busy
 [root@aldebaran ~]#

Nor did i see any "trace all block IO in the system" kind of 
functionality in blktrace. (or maybe there's one that i missed?)

> > Furthermore, various other aspects of act_log_check() itself 
> > could be expressed in terms of per tracepoint filters as well: 
> > the PID filter field for example - which is supported in the 
> > ioctl ABI but currently not exposed in the user-space blktrace 
> > utility. Same goes for the action mask which is frequently used.
> > 
> 
> Actually action mask can be specified by 'blktrace -a/-A 
> mask/mask_name'

Yes, this is what i meant by "which is frequently used".

	Ingo