From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Brian Gerst <brgerst@gmail.com>,
X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 6/6] x86/vdso: Use static_cpu_has()
Date: Mon, 25 Jan 2016 19:58:50 +0100 [thread overview]
Message-ID: <20160125185850.GD14030@pd.tnic> (raw)
In-Reply-To: <CALCETrUt42BNJEY+dskCKF8Tmwu0keMo0L-faxefMKBcKRGRFg@mail.gmail.com>
We discussed this on IRC, here's the gist:
On Mon, Jan 25, 2016 at 10:45:30AM -0800, Andy Lutomirski wrote:
> On Sun, Jan 24, 2016 at 1:28 AM, Borislav Petkov <bp@alien8.de> wrote:
> > From: Borislav Petkov <bp@suse.de>
> >
> > ... and simplify and speed up a tad.
>
> This function is only used when initializing CPUs, so the "tad" is
> very small indeed.
... except it'll pay out when the branch is patched in. Considering
that the majority of the modern CPUs out there - BSP and APs :-) - have
RDTSCP, this check will turn into a 5-byte NOP which is the most optimal
we can get. Yeah, it is still an init path so called once on each CPU
but still.
> If there are systems for which some cpus support rdtscp and some
> don't, then this patch is wrong. Of course, if the bsp has rdtscp and
> the aps don't, then we're screwed anyway.
That would be a very odd case.
> I left it as cpu_has because this is a cpu init function and it seemed
> reasonable.
Yeah, I see what you mean. But it costs us only the patching and after
that we win from not needing for fetch boot_cpu_data anymore on the APs
coming up.
Not a panties-dropper speedup but I still think it is worth the trouble.
> That being said, I have no meaningful objection to this patch.
Thanks.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
prev parent reply other threads:[~2016-01-25 18:59 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-24 9:28 [PATCH 0/6] x86/cpufeature: Cleanups and improvements v1 Borislav Petkov
2016-01-24 9:28 ` [PATCH 1/6] x86/cpufeature: Carve out X86_FEATURE_* Borislav Petkov
2016-01-24 9:28 ` [PATCH 2/6] x86/cpufeature: Replace the old static_cpu_has() with safe variant Borislav Petkov
2016-01-24 9:28 ` [PATCH 3/6] x86/cpufeature: Get rid of the non-asm goto variant Borislav Petkov
2016-01-24 9:28 ` [PATCH 4/6] x86/alternatives: Add an auxilary section Borislav Petkov
2016-01-24 9:28 ` [PATCH 5/6] x86/alternatives: Discard dynamic check after init Borislav Petkov
2016-01-24 9:28 ` [PATCH 6/6] x86/vdso: Use static_cpu_has() Borislav Petkov
2016-01-25 18:45 ` Andy Lutomirski
2016-01-25 18:58 ` Borislav Petkov [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160125185850.GD14030@pd.tnic \
--to=bp@alien8.de \
--cc=brgerst@gmail.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.