Re: [RFC PATCH 12/23] kernel/watchdog: Introduce a struct for NMI watchdog operations

From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
	Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
	Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, Borislav Petkov <bp@suse.de>,
	Tony Luck <tony.luck@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	x86@kernel.org, sparclinux@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	Jacob Pan <jacob.jun.pan@intel.com>,
	Don Zickus <dzickus@redhat.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Frederic Weisbecker <frederic@kernel.org>,
	Babu Moger <babu.moger@oracle.com>,
	"David S. Miller" <davem@davemloft.net>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Colin Ian King <colin.king@canonical.com>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	iommu@lists.linux-foundation.org
Subject: Re: [RFC PATCH 12/23] kernel/watchdog: Introduce a struct for NMI watchdog operations
Date: Wed, 13 Jun 2018 11:26:49 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1806131121180.2280@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180613084219.GT12258@hirez.programming.kicks-ass.net>

On Wed, 13 Jun 2018, Peter Zijlstra wrote:
> On Wed, Jun 13, 2018 at 05:41:41PM +1000, Nicholas Piggin wrote:
> > On Tue, 12 Jun 2018 17:57:32 -0700
> > Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote:
> > 
> > > Instead of exposing individual functions for the operations of the NMI
> > > watchdog, define a common interface that can be used across multiple
> > > implementations.
> > > 
> > > The struct nmi_watchdog_ops is defined for such operations. These initial
> > > definitions include the enable, disable, start, stop, and cleanup
> > > operations.
> > > 
> > > Only a single NMI watchdog can be used in the system. The operations of
> > > this NMI watchdog are accessed via the new variable nmi_wd_ops. This
> > > variable is set to point the operations of the first NMI watchdog that
> > > initializes successfully. Even though at this moment, the only available
> > > NMI watchdog is the perf-based hardlockup detector. More implementations
> > > can be added in the future.
> > 
> > Cool, this looks pretty nice at a quick glance. sparc and powerpc at
> > least have their own NMI watchdogs, it would be good to have those
> > converted as well.
> 
> Yeah, agreed, this looks like half a patch.

Though I'm not seeing the advantage of it. That kind of NMI watchdogs are
low level architecture details so having yet another 'ops' data structure
with a gazillion of callbacks, checks and indirections does not provide
value over the currently available weak stubs.

> > Is hpet a cross platform thing, or just x86? We should avoid
> > proliferation of files under kernel/ I think, so with these watchdog
> > driver structs then maybe implementations could go in drivers/ or
> > arch/
> 
> HPET is mostly an x86 thing (altough it can be found elsewhere), but the

On ia64 and I doubt that anyone wants to take on the task of underwater
welding it to Itanic.

> whole thing relies on the x86 NMI mechanism and is thus firmly arch/
> material (like the sparc and ppc thing).

Right. Trying to make this 'generic' is not really solving anything.

Thanks,

	tglx