From: Gabriel Krisman Bertazi <krisman@suse.de>
To: Will Deacon <will@kernel.org>
Cc: catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org,
broonie@kernel.org
Subject: Re: [RFC PATCH] arm64: Cache HW update of Access Flag support
Date: Mon, 09 Jan 2023 12:16:13 -0300 [thread overview]
Message-ID: <87lembg2ma.fsf@suse.de> (raw)
In-Reply-To: <20230106170949.GA5019@willie-the-truck> (Will Deacon's message of "Fri, 6 Jan 2023 17:09:50 +0000")
Will Deacon <will@kernel.org> writes:
> On Fri, Jan 06, 2023 at 01:38:25PM -0300, Gabriel Krisman Bertazi wrote:
>> + has_af = cpuid_feature_extract_unsigned_field(
>> + read_cpuid(ID_AA64MMFR1_EL1),
>> ID_AA64MMFR1_EL1_HAFDBS_SHIFT);
>> + return has_af;
>
> The intention here was to read the value for the _current_ CPU, since it
> might not be the same across the system when big.MISTAKE gets involved.
>
> However, since this is really just a performance optimisation and I
> think that the access flag tends to be uniformly supported in practice
> anyway, the best bet is probably just to read the sanitised version of
> the field using read_sanitised_ftr_reg().
>
> Can you give that a shot, please?
Hey Will,
Thanks for the review.
I reran the benchmark over the weekend and the impact of the bsearch
lookup seems to be <1% worse than my original patch, which is
negligible, IMO. I will shortly follow up with a v2 applying your
suggestion.
Thanks!
--
Gabriel Krisman Bertazi
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next prev parent reply other threads:[~2023-01-09 15:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-06 16:38 [RFC PATCH] arm64: Cache HW update of Access Flag support Gabriel Krisman Bertazi
2023-01-06 17:09 ` Will Deacon
2023-01-09 15:16 ` Gabriel Krisman Bertazi [this message]
2023-01-10 16:16 ` Will Deacon
2023-01-10 19:38 ` Gabriel Krisman Bertazi
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