From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>,
Ingo Molnar <mingo@kernel.org>, Uros Bizjak <ubizjak@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev, Dennis Zhou <dennis@kernel.org>,
Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op()
Date: Fri, 18 Oct 2024 15:21:39 +0300 [thread overview]
Message-ID: <ZxJS0_DUfgi4mHe1@smile.fi.intel.com> (raw)
In-Reply-To: <20241017181859.GB17263@noisy.programming.kicks-ass.net>
On Thu, Oct 17, 2024 at 08:18:59PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 16, 2024 at 12:44:18PM -0700, Dave Hansen wrote:
>
> > Would anybody hate if we broke this up a bit, like:
> >
> > const typeof(var) _val = val;
> > const int paoconst = __builtin_constant_p(val);
> > const int paoinc = paoconst && ((_val) == 1);
> > const int paodec = paoconst && ((_val) == (typeof(var))-1);
> >
> > and then did
> >
> > if (paoinc)
> > percpu_unary_op(size, qual, "inc", var);
> > ...
>
> I think that is an overall improvement. Proceed! :-)
Wouldn't typeof(var) be a regression? The val can be wider (in term of bits)
than var and cutting it like this might bring different result depending on
the signedness. TL;DR: Whatever is done, please add more (corner) test cases
to the percpu_test.c.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2024-10-18 12:21 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-05 17:03 Andy Shevchenko
2024-10-16 13:37 ` Andy Shevchenko
2024-10-16 15:44 ` Dave Hansen
2024-10-16 17:03 ` Nick Desaulniers
2024-10-16 18:06 ` Andy Shevchenko
2024-10-16 18:20 ` Andy Shevchenko
2024-10-16 19:43 ` Dave Hansen
2024-10-16 19:20 ` Peter Zijlstra
2024-10-16 19:44 ` Dave Hansen
2024-10-17 18:18 ` Peter Zijlstra
2024-10-18 12:21 ` Andy Shevchenko [this message]
2024-10-22 19:53 ` Dave Hansen
2024-10-22 23:24 ` Christoph Lameter (Ampere)
2024-10-23 17:15 ` Dave Hansen
2024-10-23 21:40 ` H. Peter Anvin
2024-10-23 14:24 ` Andy Shevchenko
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