Re: [PATCH 2/2] perf record: Add --dry-run option to check cmdline options

From: Wangnan (F)
Date: Tue Jun 21 2016 - 02:22:18 EST




On 2016/6/21 0:22, Alexei Starovoitov wrote:
On Mon, Jun 20, 2016 at 11:38:18AM -0300, Arnaldo Carvalho de Melo wrote:
Em Mon, Jun 20, 2016 at 11:29:13AM +0800, Wangnan (F) escreveu:
On 2016/6/17 0:48, Arnaldo Carvalho de Melo wrote:
Em Thu, Jun 16, 2016 at 08:02:41AM +0000, Wang Nan escreveu:
With '--dry-run', 'perf record' doesn't do reall recording. Combine with
llvm.dump-obj option, --dry-run can be used to help compile BPF objects for
embedded platform.
So these are nice and have value, but can we have a subcommand to do all
this with an expressive name, Something like:
perf bpfcc foo.c -o foo
or shorter:
perf bcc foo.c -o foo
Just like one would use gcc or some other compiler to generate something
for later use?
I'll try it today. I thought a subcommand require a bigger feature,
and wrapping clang is not big enough.
Not really, we may have as many as we like, given that they provide
something useful, like I think is the case here.

Having to edit ~/.perfconfig, create a new section, a variable in it
with a boolean value (at first, just reading the changeset comment, I
thought I had to provide a directory where to store the objects
"dumped"), to then use a tool to record a .c event, but not recording
(use dry-run, which is useful to test the command line, etc), to then
get, on the current directory, the end result looked to me a convoluted
way to ask perf to compile the given .c file into a .o for later use.

Doing:

perf bcc -c foo.c

Looks so much simpler and similar to an existing compile source code
into object file workflow (gcc's, any C compiler) that I think it would
fit in the workflow being discussed really nicely.
I'm hopeful that eventually we'll be able merge iovisor/bcc project
with perf, so would be good to reserve 'perf bcc' command for that
future use. Also picking a different name for compiling would be less
confusing to users who already familiar with bcc. Instead we can use:
perf bpfcc foo.c -o foo.o
perf cc foo.c
perf compile foo.c


I think finally we should make perf independent with LLVM runtime.
I suggest 'perf bpf' subcommand to deal with all BPF related things,
include compiling, configuration and potential cache.

Thank you.