From: Stefan Hajnoczi <stefanha@gmail.com>
To: Amit Shah <amit.shah@redhat.com>
Cc: qemu list <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH (resend, rebase) 3/3] virtio-serial: Enable ioeventfd
Date: Mon, 28 Feb 2011 15:28:49 +0000 [thread overview]
Message-ID: <AANLkTinrtaktYPPhcrz_yCvA8vEOHbND8CiO8h+PH_vD@mail.gmail.com> (raw)
In-Reply-To: <0948831a888a7047d9e1ce945197a0210c922b1b.1298891447.git.amit.shah@redhat.com>
On Mon, Feb 28, 2011 at 11:12 AM, Amit Shah <amit.shah@redhat.com> wrote:
> Enable ioeventfd for virtio-serial devices by default. Commit
> 25db9ebe15125deb32958c6df74996f745edf1f9 lists the benefits of using
> ioeventfd.
>
> Copying a file from guest to host over a virtio-serial channel didn't
> show much difference in time or io_exit rate.
The cost of enabling ioeventfd is one eventfd file descriptor and KVM
in-kernel device slot per virtqueue. The current maximum number per
VM is 200, this is a kernel limit in
include/linux/kvm_host.h:NR_IOBUS_DEVS.
Do you really want to use ioeventfd for virtio-serial? Perhaps this
is more useful for high-frequency device interfaces.
Stefan
next prev parent reply other threads:[~2011-02-28 15:28 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-28 11:12 [Qemu-devel] [PULL (resend, rebase) 0/3] virtio-serial fixes, ioeventfd support Amit Shah
2011-02-28 11:12 ` [Qemu-devel] [PATCH (resend, rebase) 1/3] virtio-serial: Use a struct to pass config information from proxy Amit Shah
2011-02-28 11:12 ` [Qemu-devel] [PATCH (resend, rebase) 2/3] virtio-serial: Disallow generic ports at id 0 Amit Shah
2011-02-28 11:12 ` [Qemu-devel] [PATCH (resend, rebase) 3/3] virtio-serial: Enable ioeventfd Amit Shah
2011-02-28 15:28 ` Stefan Hajnoczi [this message]
2011-03-01 6:41 ` Amit Shah
2011-03-01 10:23 ` Stefan Hajnoczi
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