linux-kernel - Re: Alternatives to /sys/kernel/debug/wakeup

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Message-ID: <20190619170750.GB10107@kroah.com>
Date:   Wed, 19 Jun 2019 19:07:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Tri Vo <trong@...roid.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Sandeep Patil <sspatil@...roid.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexei Starovoitov <ast@...com>
Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources

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