From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>,
"Denis V. Lunev" <den-lists@parallels.com>
Cc: QEMU Trivial <qemu-trivial@nongnu.org>,
Tiejun Chen <tiejun.chen@intel.com>,
QEMU Developers <qemu-devel@nongnu.org>,
kvm-devel <kvm@vger.kernel.org>
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] kvm_irqchip_assign_irqfd: just set irqfd in case of kvm_irqfds_enabled()
Date: Sat, 27 Dec 2014 15:52:12 +0100 [thread overview]
Message-ID: <549EC79C.2090608@redhat.com> (raw)
In-Reply-To: <CAFEAcA_DTVFUE5QmU3T8DbuZQwhcXPhuxVfEYOTyST3sDL0-PQ@mail.gmail.com>
On 26/12/2014 18:59, Peter Maydell wrote:
> Mm, but once you're into such microoptimisations as this you really
> need to have a good justification for the effort, in the form of
> profiling measurements that indicate that this is a hot path.
> In this case that seems pretty unlikely, because I'd expect all
> the systems where we care about performance will support irqfds,
> so we won't be taking the early-exit code path anyhow. (And
> not supporting irqfds is leaving much more performance on the
> table than we could possibly be talking about in this function.)
Also, it's even possible for a compiler to figure this out. All in all,
I don't see any advantage to this patch...
Paolo
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>,
"Denis V. Lunev" <den-lists@parallels.com>
Cc: QEMU Trivial <qemu-trivial@nongnu.org>,
Tiejun Chen <tiejun.chen@intel.com>,
QEMU Developers <qemu-devel@nongnu.org>,
kvm-devel <kvm@vger.kernel.org>
Subject: Re: [PATCH] kvm_irqchip_assign_irqfd: just set irqfd in case of kvm_irqfds_enabled()
Date: Sat, 27 Dec 2014 15:52:12 +0100 [thread overview]
Message-ID: <549EC79C.2090608@redhat.com> (raw)
In-Reply-To: <CAFEAcA_DTVFUE5QmU3T8DbuZQwhcXPhuxVfEYOTyST3sDL0-PQ@mail.gmail.com>
On 26/12/2014 18:59, Peter Maydell wrote:
> Mm, but once you're into such microoptimisations as this you really
> need to have a good justification for the effort, in the form of
> profiling measurements that indicate that this is a hot path.
> In this case that seems pretty unlikely, because I'd expect all
> the systems where we care about performance will support irqfds,
> so we won't be taking the early-exit code path anyhow. (And
> not supporting irqfds is leaving much more performance on the
> table than we could possibly be talking about in this function.)
Also, it's even possible for a compiler to figure this out. All in all,
I don't see any advantage to this patch...
Paolo
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>,
"Denis V. Lunev" <den-lists@parallels.com>
Cc: QEMU Trivial <qemu-trivial@nongnu.org>,
Tiejun Chen <tiejun.chen@intel.com>,
QEMU Developers <qemu-devel@nongnu.org>,
kvm-devel <kvm@vger.kernel.org>
Subject: Re: [Qemu-devel] [PATCH] kvm_irqchip_assign_irqfd: just set irqfd in case of kvm_irqfds_enabled()
Date: Sat, 27 Dec 2014 15:52:12 +0100 [thread overview]
Message-ID: <549EC79C.2090608@redhat.com> (raw)
In-Reply-To: <CAFEAcA_DTVFUE5QmU3T8DbuZQwhcXPhuxVfEYOTyST3sDL0-PQ@mail.gmail.com>
On 26/12/2014 18:59, Peter Maydell wrote:
> Mm, but once you're into such microoptimisations as this you really
> need to have a good justification for the effort, in the form of
> profiling measurements that indicate that this is a hot path.
> In this case that seems pretty unlikely, because I'd expect all
> the systems where we care about performance will support irqfds,
> so we won't be taking the early-exit code path anyhow. (And
> not supporting irqfds is leaving much more performance on the
> table than we could possibly be talking about in this function.)
Also, it's even possible for a compiler to figure this out. All in all,
I don't see any advantage to this patch...
Paolo
next prev parent reply other threads:[~2014-12-27 14:52 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-26 8:05 [Qemu-trivial] [PATCH] kvm_irqchip_assign_irqfd: just set irqfd in case of kvm_irqfds_enabled() Tiejun Chen
2014-12-26 8:05 ` [Qemu-devel] " Tiejun Chen
2014-12-26 8:05 ` Tiejun Chen
2014-12-26 10:00 ` [Qemu-trivial] [Qemu-devel] " Peter Maydell
2014-12-26 10:00 ` Peter Maydell
2014-12-26 10:00 ` Peter Maydell
2014-12-26 10:16 ` [Qemu-trivial] " Denis V. Lunev
2014-12-26 10:16 ` Denis V. Lunev
2014-12-26 10:16 ` Denis V. Lunev
2014-12-26 17:59 ` [Qemu-trivial] [Qemu-devel] " Peter Maydell
2014-12-26 17:59 ` Peter Maydell
2014-12-26 17:59 ` Peter Maydell
2014-12-27 14:52 ` Paolo Bonzini [this message]
2014-12-27 14:52 ` Paolo Bonzini
2014-12-27 14:52 ` Paolo Bonzini
2014-12-29 1:31 ` [Qemu-trivial] [Qemu-devel] " Chen, Tiejun
2014-12-29 1:31 ` Chen, Tiejun
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