linux-kernel - Re: [PATCH v2 1/3] drivers: hv: vmbus: Introduce latency testing

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Date:   Fri, 23 Aug 2019 13:36:33 -0400
From:   Branden Bonaby <brandonbonaby94@...il.com>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] drivers: hv: vmbus: Introduce latency testing

On Fri, Aug 23, 2019 at 04:44:09PM +0000, Michael Kelley wrote:
> From: Branden Bonaby <brandonbonaby94@...il.com> Sent: Thursday, August 22, 2019 8:39 PM
> > > > diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> > > > index 09829e15d4a0..c9c63a4033cd 100644
> > > > --- a/drivers/hv/connection.c
> > > > +++ b/drivers/hv/connection.c
> > > > @@ -357,6 +357,9 @@ void vmbus_on_event(unsigned long data)
> > > >
> > > >  	trace_vmbus_on_event(channel);
> > > >
> > > > +#ifdef CONFIG_HYPERV_TESTING
> > > > +	hv_debug_delay_test(channel, INTERRUPT_DELAY);
> > > > +#endif /* CONFIG_HYPERV_TESTING */
> > >
> > > You are following Vitaly's suggestion to use #ifdef's so no code is
> > > generated when HYPERV_TESTING is not enabled.  However, this
> > > direct approach to using #ifdef's really clutters the code and makes
> > > it harder to read and follow.  The better approach is to use the
> > > #ifdef in the include file where the functions are defined.  If
> > > HYPERV_TESTING is not enabled, provide a #else that defines
> > > the function with an empty implementation for which the compiler
> > > will generate no code.   An as example, see the function definition
> > > for hyperv_init() in arch/x86/include/asm/mshyperv.h.  There are
> > > several functions treated similarly in that include file.
> > >
> > 
> > I checked out the code in arch/x86/include/asm/mshyperv.h, after
> > thinking about it, I'm wondering if it would be better just to have
> > two files one called hv_debugfs.c and the other hyperv_debugfs.h.
> > I could put the code definitions in hv_debugfs.c and at the top
> > include the hyperv_debugfs.h file which would house the declarations
> > of these functions under the ifdef. Then like you alluded too use
> > an #else statement that would have the null implementations of the
> > above functions. Then put an #include "hyperv_debugfs.h" in the
> > hyperv_vmbus.h file. I figured instead of putting the code directly
> > into the vmbus_drv.c file it might be best to put them in a seperate
> > file like hv_debugfs.c. This way when we start adding more tests we
> > don't bloat the vmbus_drv.c file unnecessarily. The hv_debugfs.c
> > file would have the #ifdef CONFIG_HYPERV_TESTING at the top so if
> > its not enabled  those null implementations in "hyperv_debugfs.h"
> > woud kick in anywhere that included the hyperv_vmbus.h file which
> > is what we want.
> > 
> > what do you think?
> > 
> 
> I'll preface my comments by saying that how code gets structured
> into files is always a bit of a judgment call.  The goal is to group code
> into sensible chunks to make it easy to understand and to make it
> easy to modify and extend later.  The latter is a prediction about the
> future, which may or may not be accurate.   For the former, what's
> "easy to understand," is often in the eye of the beholder.  So you may
> get different opinions from different reviewers.
> 
> That said, I like the idea of a separate hv_debugfs.c file to contain
> the implementation of the various functions you have added to
> provide the fuzzing capability.   I'm less convinced about the value
> of a separate hyperv_debugfs.h file.   I think you have one big
> #ifdef CONFIG_HYPERV_TESTING followed by the declarations of
> the functions in hv_debugfs.c, followed by #else and null
> implementations of those functions.  This is 20 lines of code or so,
> and could easily go in hyperv_vmbus.h.
> 
> For the new hv_debugfs.c, you can avoid the need for
> #ifdef CONFIG_HYPERV_TESTING by modifying the Makefile in
> drivers/hv so that hv_debugfs.o is built only if CONFIG_HYPERV_TESTING
> is defined.  Look at the current Makefile to see how this is done
> with CONFIG_HYPERV_UTILS and CONFIG_HYPERV_BALLOON.
> 
> Michael
>

I see, that does make sense, I'll go ahead and add these changes.

thanks

branden bonaby