linux-kernel - Re: [PATCH] cpupower: add Makefile dependencies for install targets

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Date:   Thu, 07 Jan 2021 21:59:51 +0100
From:   Thomas Renninger <trenn@...e.com>
To:     Ivan Babrou <ivan@...udflare.com>
Cc:     linux-pm@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...udflare.com>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH] cpupower: add Makefile dependencies for install targets

Am Donnerstag, 7. Januar 2021, 18:42:25 CET schrieb Ivan Babrou:
> On Thu, Jan 7, 2021 at 2:07 AM Thomas Renninger <trenn@...e.com> wrote:
> > Am Dienstag, 5. Januar 2021, 00:57:18 CET schrieb Ivan Babrou:
> > > This allows building cpupower in parallel rather than serially.
> > 
> > cpupower is built serially:
> > 
> > [ make clean ]
> > 
> > time make
> > real    0m3,742s
> > user    0m3,330s
> > sys     0m1,105s
> > 
> > [ make clean ]
> > 
> > time make -j10
> > real    0m1,045s
> > user    0m3,153s
> > sys     0m1,037s
> > 
> > Only advantage I see is that you can call
> > make install-xy
> > targets without calling the corresponding build target
> > make xy
> > similar to the general install target:
> > install: all install-lib ...
> > 
> > Not sure anyone needs this and whether all targets
> > successfully work this way.
> > If you'd show a useful usecase example...
> 
> We build a bunch of kernel related tools (perf, cpupower, bpftool,
> etc.) from our own top level Makefile, propagating parallelism
> downwards like one should.
I still do not understand why you do not simply build:
Also if I call this from /tools directory I get a quick build:
make -j20 cpupower

Can you please show the make calls, ideally with a timing to better understand
and also to reproduce the advantages this patch introduces.
>From what I can see, it only helps if one calls "sub-install" targets 
directly?
And I still do not understand why things should be more parallel now.

> Without this patch we have to remove parallelism for cpupower,
Why?

> which doesn't seem like a very clean thing
> to do, especially if you consider that it's 3x faster with parallelism
> enabled in wall clock terms.
Sure, you want to build in parallel. I still do not understand how this
patch helps in this regard.

BTW, I recently had a bunch of userspace tools Makefile patches.
I'd like to add you to CC for a review if they are not submitted already.

    Thomas