Re: [PATCH V7 01/18] perf/core: Use static_call to optimize perf_guest_info_callbacks

From: Joe Perches <joe@perches.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Zhu Lingshan <lingshan.zhu@intel.com>,
	 wanpengli@tencent.com, Like Xu <like.xu@linux.intel.com>,
	eranian@google.com,  weijiang.yang@intel.com,
	Guo Ren <guoren@kernel.org>,
	 linux-riscv@lists.infradead.org, Will Deacon <will@kernel.org>,
	 kvmarm@lists.cs.columbia.edu, kan.liang@linux.intel.com,
	ak@linux.intel.com,  kvm@vger.kernel.org,
	Marc Zyngier <maz@kernel.org>,
	joro@8bytes.org,  x86@kernel.org, linux-csky@vger.kernel.org,
	wei.w.wang@intel.com,  xen-devel@lists.xenproject.org,
	liuxiangdong5@huawei.com, bp@alien8.de,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	 linux-arm-kernel@lists.infradead.org, jmattson@google.com,
	 like.xu.linux@gmail.com, Nick Hu <nickhu@andestech.com>,
	seanjc@google.com,  linux-kernel@vger.kernel.org,
	pbonzini@redhat.com, vkuznets@redhat.com
Subject: Re: [PATCH V7 01/18] perf/core: Use static_call to optimize perf_guest_info_callbacks
Date: Fri, 02 Jul 2021 09:56:51 -0700	[thread overview]
Message-ID: <7a2ef915bd08a1c0277b9633e20905c0ca62c568.camel@perches.com> (raw)
In-Reply-To: <20210702163836.GB94260@C02TD0UTHF1T.local>

On Fri, 2021-07-02 at 17:38 +0100, Mark Rutland wrote:
> On Fri, Jul 02, 2021 at 09:00:22AM -0700, Joe Perches wrote:
> > On Fri, 2021-07-02 at 13:22 +0200, Peter Zijlstra wrote:
> > > On Tue, Jun 22, 2021 at 05:42:49PM +0800, Zhu Lingshan wrote:
[]
> > > > +	if (perf_guest_cbs && perf_guest_cbs->handle_intel_pt_intr)
> > > > +		static_call_update(x86_guest_handle_intel_pt_intr,
> > > > +				   perf_guest_cbs->handle_intel_pt_intr);
> > > > +}
> > > 
> > > Coding style wants { } on that last if().
> > 
> > That's just your personal preference.
> > 
> > The coding-style document doesn't require that.
> > 
> > It just says single statement.  It's not the number of
> > vertical lines or characters required for the statement.
> > 
> > ----------------------------------
> > 
> > Do not unnecessarily use braces where a single statement will do.
> > 
> > .. code-block:: c
> > 
> > 	if (condition)
> > 		action();
> > 
> > and
> > 
> > .. code-block:: none
> > 
> > 	if (condition)
> > 		do_this();
> > 	else
> > 		do_that();
> > 
> > This does not apply if only one branch of a conditional statement is a single
> > statement; in the latter case use braces in both branches:
> 
> Immediately after this, we say:
> 
> > Also, use braces when a loop contains more than a single simple statement:
> > 
> > .. code-block:: c
> > 
> >         while (condition) {
> >                 if (test)
> >                         do_something();
> >         }
> > 
> 
> ... and while that says "a loop", the principle is obviously supposed to
> apply to conditionals too; structurally they're no different. We should
> just fix the documentation to say "a loop or conditional", or something
> to that effect.

<shrug>  Maybe.

I think there are _way_ too many existing obvious uses where the
statement that follows a conditional is multi-line.

	if (foo)
		printk(fmt,
		       args...);

where the braces wouldn't add anything other than more vertical space.

I don't much care one way or another other than Peter's somewhat ambiguous
use of the phrase "coding style".

checkpatch doesn't emit a message either way.
-----------------------------------------
$ cat t_multiline.c
// SPDX-License-Identifier: GPL-2.0-only

void foo(void)
{
	if (foo) {
		pr_info(fmt,
			args);
	}

	if (foo)
		pr_info(fmt,
			args);

	if (foo)
		pr_info(fmt, args);
}

$ ./scripts/checkpatch.pl -f --strict t_multiline.c
total: 0 errors, 0 warnings, 0 checks, 16 lines checked

t_multiline.c has no obvious style problems and is ready for submission.
-----------------------------------------

cheers, Joe

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