Re: tracepoints in ext4 (and/or ext3?)

Eric Sandeen
2008-08-12T14:02:40Z

Jose R. Santos wrote:
> On Mon, 11 Aug 2008 15:18:07 -0500
> Eric Sandeen <sandeen@redhat.com> wrote:
>
>> As just an initial inquiry, I'm wondering how people would feel about
>> putting some tracepoints (trace_mark()) into ext[34] for monitoring the
>> fs behavior.
>>
>> Good/bad/indifferent?
>>
>> Thanks,
>>
>> -Eric
>
> Good idea, although Im not sure if ext[34] is the best place we should
> start putting markers though.

Sure, but there have already been patches floated for the vfs, and ...

> For ext[34], I would start by putting markers on VFS entry points into
> ext4 and journal activity. For these to be useful though, we also need
> markers in the following places:
>
> iochedulers
> elv_next_request()
> elv_add_request()
> elv_completed_request()

I think there's talk of changing the blktrace infrastructure to use markers.

> scsi
> scsi_prep_fn()
> scsi_dispatch_cmd()
> scsi_done()
> scsi_io_completion()
>
> Entry and exit points of all IO system calls.
> AND
> The VFS call for these system calls.

http://lists-archives.org/linux-kernel/16489694-lttng-tracepoint-instrumentation-fs.html

> bio
> generic_make_request()
> bio_endio()
>
> Scheduler
> idle_balance() Personally, I find it useful to know when a
> machine goes idle because is stalling on IO
>
>
> Im sure Im missing something but this should be a good start to be able
> to track the life of a pending IO to see where deficiencies lie.

Yep, this all sounds good.

Thanks,
-Eric