From: Ingo Molnar <mingo@kernel.org>
To: Nadav Amit <namit@cs.technion.ac.il>
Cc: pbonzini@redhat.com, hpa@zytor.com, mingo@redhat.com,
tglx@linutronix.de, x86@kernel.org, kvm@vger.kernel.org,
nadav.amit@gmail.com, linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 0/3] x86: structs for cpuid info in x86
Date: Tue, 16 Sep 2014 15:22:27 +0200 [thread overview]
Message-ID: <20140916132226.GA13726@gmail.com> (raw)
In-Reply-To: <1410870160-28845-1-git-send-email-namit@cs.technion.ac.il>
* Nadav Amit <namit@cs.technion.ac.il> wrote:
> The code that deals with x86 cpuid fields is hard to follow since it performs
> many bit operations and does not refer to cpuid field explicitly. To
> eliminate the need of openning a spec whenever dealing with cpuid fields, this
> patch-set introduces structs that reflect the various cpuid functions.
>
> Thanks for reviewing the patch-set.
>
> Nadav Amit (3):
> x86: Adding structs to reflect cpuid fields
> x86: Use new cpuid structs in cpuid functions
> KVM: x86: Using cpuid structs in KVM
>
> arch/x86/include/asm/cpuid_def.h | 163 +++++++++++++++++++++++++++++++++++++++
> arch/x86/kernel/cpu/common.c | 56 ++++++++------
> arch/x86/kvm/cpuid.c | 36 +++++----
> 3 files changed, 219 insertions(+), 36 deletions(-)
> create mode 100644 arch/x86/include/asm/cpuid_def.h
I personally like bitfields in theory (they provide type clarity
and abstract robustness, compared to open-coded bitmask numeric
literals that are often used in cpuid using code, obfuscating
cpuid usage), with the big caveat that for many years I didn't
like bitfields in practice: older versions of GCC did a really
poor job of optimizing them.
So such a series would only be acceptable if it's demonstrated
that both 'latest' and 'reasonably old' GCC versions do a good
job in that department, compared to the old open-coded bitmask
ops ...
Comparing the 'size vmlinux' output of before/after kernels would
probably be a good start in seeing the impact of such a change.
If those results are positive then this technique could be
propagated to all cpuid using code in arch/x86/, of which
there's plenty.
Thanks,
Ingo
next parent reply other threads:[~2014-09-16 13:22 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1410870160-28845-1-git-send-email-namit@cs.technion.ac.il>
2014-09-16 13:22 ` Ingo Molnar [this message]
2014-09-16 20:19 ` [PATCH 0/3] x86: structs for cpuid info in x86 Nadav Amit
2014-09-17 12:37 ` Ingo Molnar
2014-09-17 12:45 ` Borislav Petkov
2014-09-17 12:54 ` [RESEND PATCH " Nadav Amit
2014-09-17 12:54 ` [RESEND PATCH 1/3] x86: Adding structs to reflect cpuid fields Nadav Amit
2014-09-17 13:21 ` Borislav Petkov
2014-09-17 13:53 ` Nadav Amit
2014-09-17 14:06 ` Borislav Petkov
2014-09-17 15:04 ` Radim Krčmář
2014-09-17 15:22 ` Borislav Petkov
2014-09-18 0:29 ` Radim Krčmář
2014-09-18 7:19 ` Borislav Petkov
2014-09-18 10:00 ` Radim Krčmář
2014-09-18 13:06 ` Paolo Bonzini
2014-09-18 13:26 ` Borislav Petkov
2014-09-18 13:36 ` Paolo Bonzini
2014-09-19 7:58 ` Borislav Petkov
2014-09-19 8:59 ` Nadav Amit
2014-09-19 10:32 ` Borislav Petkov
2014-09-19 13:40 ` Paolo Bonzini
2014-09-19 14:44 ` Borislav Petkov
2014-09-17 14:10 ` Peter Zijlstra
2014-09-17 12:54 ` [RESEND PATCH 2/3] x86: Use new cpuid structs in cpuid functions Nadav Amit
2014-09-17 12:54 ` [RESEND PATCH 3/3] KVM: x86: Using cpuid structs in KVM Nadav Amit
2014-09-17 14:12 ` [PATCH 0/3] x86: structs for cpuid info in x86 Peter Zijlstra
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