linux-kernel - Re: [PATCH v2] staging: greybus: use inline function for macros

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Message-ID: <ZByskk59KaEZbc6+@ubun2204.myguest.virtualbox.org>
Date:   Fri, 24 Mar 2023 01:16:26 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Julia Lawall <julia.lawall@...ia.fr>, Alex Elder <elder@...e.org>,
        Menna Mahmoud <eng.mennamahmoud.mm@...il.com>,
        outreachy@...ts.linux.dev, johan@...nel.org, elder@...nel.org,
        linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH v2] staging: greybus: use inline function for macros

On Thu, Mar 23, 2023 at 06:22:55AM +0100, Greg KH wrote:
> On Thu, Mar 23, 2023 at 10:35:59AM +0530, Deepak R Varma wrote:
> > On Thu, Mar 23, 2023 at 05:58:02AM +0100, Greg KH wrote:
> > > Nice, that shows that it is the same both ways as the compiler version
> > > you are using is smart enough
> > > 
> > > Which compiler and version is this?  Does it work the same for all of
> > > the supported versions we have to support (i.e. really old gcc?)
> > > 
> > > For the most part, sysfs files are not on any sort of "fast path" so a
> > 
> > Hello,
> > Is there a guideline/documentation on how to identify if a code is part of
> > fast/slow path?
> 
> Not really, the general rule is if the code is used in a function that
> is time criticial, then it is in the "fast path".
> 
> Normally the code path for I/O or for determining what process to
> schedule next is a "fast path" as you want to do the least amount of
> work in the kernel so as to get the I/O to the hardware or caller, or
> you want to schedule the next process faster so that it can do the real
> work that is wanted.
> 
> But for some I/O, where the hardware is the limiting factor (like slow
> USB or serial connections), no matter how optimized the kernel is, the
> data can not get to the user any faster because the hardware just can
> not provide it, so for that, it's not really that critical.
> 
> Note that "time critical" can change depending on the user of the system
> and as hardware evolves.
> 
> One example would be the creation of a number of sysfs entries for the
> disks in the systems.  On a "normal" system, creating them all is trivial
> as there are not many disks.  But on some "big" systems with many tens
> of thousands of disks, it can become a boot time bottleneck.
> 
> So it's usually "you know it when you see it show up on a profile", use
> the perf tool to test your workload on, to see where in the kernel
> things are taking up too much time so you know what needs to be made
> faster.
> 
> hope this helps,

Thank you Greg.
Yes, it definitely is very helpful. I sincerely appreciate the explanation and
the time you took to write it in so detail. I am Obliged.

Regards,
Deepak.


> 
> greg k-h