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From: Mark Rutland <mark.rutland@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, ardb@kernel.org,
	james.morse@arm.com, joey.gouly@arm.com, maz@kernel.org,
	will@kernel.org
Subject: Re: [PATCH v2 7/8] arm64: alternatives: add alternative_has_feature_*()
Date: Sat, 17 Sep 2022 13:52:04 +0100	[thread overview]
Message-ID: <YyXC9CLeKujA5zYo@FVFF77S0Q05N> (raw)
In-Reply-To: <YyRaUMHVngv9arE4@arm.com>

On Fri, Sep 16, 2022 at 12:13:20PM +0100, Catalin Marinas wrote:
> On Mon, Sep 12, 2022 at 05:22:09PM +0100, Mark Rutland wrote:
> > @@ -465,7 +464,7 @@ static __always_inline bool __cpus_have_const_cap(int num)
> >  {
> >  	if (num >= ARM64_NCAPS)
> >  		return false;
> > -	return static_branch_unlikely(&cpu_hwcap_keys[num]);
> > +	return alternative_has_feature_unlikely(num);
> >  }
> 
> I wonder whether we should move this to "likely" (as a subsequent
> patch). It would save a branch as new CPUs turn up supporting the new
> features. We may want to keep errata workarounds as "unlikely" though as
> they tend not to stick around in future CPUs.

I had assumed we'd add separate likely/unlikely forms that we can use
independently per feature or callsite (since e.g. we want any errata caps to be
unlikely); if we have specific cases we'd like to change I can go spin that
shortly.

Thanks,
Mark.

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  reply	other threads:[~2022-09-17 12:53 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-12 16:22 [PATCH v2 0/8] arm64: alternatives: improvements Mark Rutland
2022-09-12 16:22 ` [PATCH v2 1/8] arm64: cpufeature: make cpus_have_cap() noinstr-safe Mark Rutland
2022-09-12 16:22 ` [PATCH v2 2/8] arm64: alternatives: kvm: prepare for cap changes Mark Rutland
2022-09-12 16:22 ` [PATCH v2 3/8] arm64: alternatives: proton-pack: " Mark Rutland
2022-09-12 16:22 ` [PATCH v2 4/8] arm64: alternatives: hoist print out of __apply_alternatives() Mark Rutland
2022-09-12 16:22 ` [PATCH v2 5/8] arm64: alternatives: make alt_region const Mark Rutland
2022-09-12 16:22 ` [PATCH v2 6/8] arm64: alternatives: have callbacks take a cap Mark Rutland
2022-09-27  9:31   ` Jon Hunter
2022-09-27  9:31     ` Jon Hunter
2022-09-29  9:53     ` Jon Hunter
2022-09-29  9:53       ` Jon Hunter
2022-09-29 10:10       ` Ard Biesheuvel
2022-09-29 10:10         ` Ard Biesheuvel
2022-09-29 10:48         ` Jon Hunter
2022-09-29 10:48           ` Jon Hunter
2022-09-29 10:47       ` Mark Rutland
2022-09-29 10:47         ` Mark Rutland
2022-09-29 11:01         ` Jon Hunter
2022-09-29 11:01           ` Jon Hunter
2022-09-29 11:09           ` Mark Rutland
2022-09-29 11:09             ` Mark Rutland
2022-09-29 13:37             ` Jon Hunter
2022-09-29 13:37               ` Jon Hunter
2022-09-29 14:38               ` Mark Rutland
2022-09-29 14:38                 ` Mark Rutland
2022-09-12 16:22 ` [PATCH v2 7/8] arm64: alternatives: add alternative_has_feature_*() Mark Rutland
2022-09-16 11:13   ` Catalin Marinas
2022-09-17 12:52     ` Mark Rutland [this message]
2022-09-19 17:01   ` Nathan Chancellor
2022-09-19 17:01     ` Nathan Chancellor
2022-09-20 12:09     ` Mark Rutland
2022-09-20 12:09       ` Mark Rutland
2022-09-20 13:31       ` Nathan Chancellor
2022-09-20 13:31         ` Nathan Chancellor
2022-09-12 16:22 ` [PATCH v2 8/8] arm64: alternatives: add shared NOP callback Mark Rutland
2022-09-13 13:36 ` [PATCH v2 0/8] arm64: alternatives: improvements Ard Biesheuvel
2022-09-16 17:46 ` Catalin Marinas
2022-09-17 12:46   ` Mark Rutland

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