From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Vijay Kilari <vijay.kilari@gmail.com>,
Liang Li <liang.z.li@intel.com>,
QEMU Developers <qemu-devel@nongnu.org>,
Adam Richter <adamrichter4@gmail.com>,
qemu-arm <qemu-arm@nongnu.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH 0/7] Improve buffer_is_zero
Date: Wed, 24 Aug 2016 07:45:15 -0400 (EDT) [thread overview]
Message-ID: <2076948386.5196666.1472039115921.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <CAFEAcA9EkuHT4uV8RS1-ZaJBWWNrs87sGkmvhw0MfWGcAg4eoQ@mail.gmail.com>
> On 24 August 2016 at 11:26, Adam Richter <adamrichter4@gmail.com> wrote:
> > I hope that that consideration, combined with the micro-costs to
> > readability and portability of using and ELF specific and perhaps
> > currently GCC specific feature might tip the balance against the
> > savings of a level of function call indirection that I assume the use
> > of ifunc was intended to provide.
>
> It doesn't actually save a level of indirection -- if you single step
> through an ifunc call it goes via some ELF section. The thing it
> does save is that you don't pay the cost of figuring out the right
> ifunc to use on this system at startup, but only when the ifunc call
> path is first used. That's useful for a big thing like glibc which
> might have lots of ifuncs and not want to pay a big startup cost,
> but for QEMU there's really no need given we only have one...
It does save a level of indirection after the first call AFAIK, but
it shouldn't be measurable.
Paolo
next prev parent reply other threads:[~2016-08-24 11:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-24 4:17 [Qemu-arm] [PATCH 0/7] Improve buffer_is_zero Richard Henderson
2016-08-24 4:17 ` [Qemu-devel] [PATCH 1/7] cutils: Remove SPLAT macro Richard Henderson
2016-08-24 4:17 ` [Qemu-devel] [PATCH 2/7] cutils: Export only buffer_is_zero Richard Henderson
2016-08-24 8:37 ` [Qemu-arm] " Dr. David Alan Gilbert
2016-08-24 4:17 ` [Qemu-devel] [PATCH 3/7] cutils: Rearrange buffer_is_zero acceleration Richard Henderson
2016-08-24 4:17 ` [Qemu-devel] [PATCH 4/7] cutils: Add generic prefetch Richard Henderson
2016-08-24 4:17 ` [Qemu-arm] [PATCH 5/7] cutils: Rewrite x86 buffer zero checking Richard Henderson
2016-08-24 4:17 ` [Qemu-arm] [PATCH 6/7] cutils: Rewrite aarch64 " Richard Henderson
2016-08-24 4:17 ` [Qemu-arm] [PATCH 7/7] cutils: Rewrite ppc " Richard Henderson
2016-08-24 4:30 ` [Qemu-arm] [Qemu-devel] [PATCH 0/7] Improve buffer_is_zero no-reply
2016-08-24 4:38 ` [Qemu-arm] " Paolo Bonzini
2016-08-24 14:53 ` [Qemu-arm] [Qemu-devel] " Richard Henderson
2016-08-24 14:59 ` Paolo Bonzini
2016-08-24 8:34 ` Dr. David Alan Gilbert
2016-08-24 10:26 ` Adam Richter
2016-08-24 10:52 ` [Qemu-arm] " Peter Maydell
2016-08-24 11:45 ` Paolo Bonzini [this message]
2016-08-24 12:22 ` Peter Maydell
2016-08-25 6:37 ` [Qemu-arm] " Vijay Kilari
2016-08-25 8:04 ` Vijay Kilari
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