Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 19 Jun 2019 19:07:50 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Joel Fernandes <joelaf@google.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Tri Vo <trong@android.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Sandeep Patil <sspatil@android.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Hridya Valsaraju <hridya@google.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Alexei Starovoitov <ast@fb.com>
Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources
Message-ID: <20190619170750.GB10107@kroah.com>
References: <CANA+-vCThdRivg7nrMK5QoFu8SGUzEVSvSyp0H2CPyy9==Tqog@mail.gmail.com>
 <CANA+-vARQ9Ao=W1oEArrAQ0sqh757orq=-=kytdVPhstm-3E9w@mail.gmail.com>
 <20190618182502.GC203031@google.com>
 <4587569.x9DSL43cXO@kreacher>
 <CANA+-vCMK6u1n9gXf2+v5dFn_tGfr1PT8d7W4d2BCzw+B-HvYw@mail.gmail.com>
 <CAJWu+oo7kwmEyMXQN0yfswV2=J-Fa9QybhAUx-SOGG_ipsBErQ@mail.gmail.com>
 <CAJZ5v0gvzCx-7qS9qkxB=sGKjQJKMR7yCc21f=_vqrbZxMSWNg@mail.gmail.com>
 <CAJWu+oqSgcBVhDY7CjWpNQrK=XiKAb5S-YSp=6-UM--UFmKvGQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAJWu+oqSgcBVhDY7CjWpNQrK=XiKAb5S-YSp=6-UM--UFmKvGQ@mail.gmail.com>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jun 19, 2019 at 12:53:12PM -0400, Joel Fernandes wrote:
> > It is conceivable to have a "wakeup_sources" directory under
> > /sys/power/ and sysfs nodes for all wakeup sources in there.
> 
> One of the "issues" with this is, now if you have say 100 wake up
> sources, with 10 entries each, then we're talking about a 1000 sysfs
> files. Each one has to be opened, and read individually. This adds
> overhead and it is more convenient to read from a single file. The
> problem is this single file is not ABI. So the question I guess is,
> how do we solve this in both an ABI friendly way while keeping the
> overhead low.

How much overhead?  Have you measured it, reading from virtual files is
fast :)

And how often does this happen?  Does it _need_ to happen?

Parsing files is also hard, and not for sysfs files, you can't have it
both ways.

So try it this way, and if there really is a performance issue, we can
then talk about it...

thanks,

greg k-h