From: Stephen Hemminger <stephen@networkplumber.org>
To: James Yu <ypyu2011@gmail.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] outw() in virtio_ring_doorbell() in DPDK+virtio consume 40% of the CPU in oprofile
Date: Mon, 16 Dec 2013 15:58:18 -0800 [thread overview]
Message-ID: <20131216155818.5a422aa4@nehalam.linuxnetplumber.net> (raw)
In-Reply-To: <CAFMB=kBTzbYWvEG9qsdhU7u2Jzh_wZid4vcrenK_XX8A-eqckA@mail.gmail.com>
On Mon, 16 Dec 2013 15:35:27 -0800
James Yu <ypyu2011@gmail.com> wrote:
> (A) The packets I sent are 64-bytes, not big packet. I am not sure GSO will
> help. For bigger packet, it will help.
It will not help with small packets.
> (B) What you do mean "multiple packets per second" ? Do you mean multiple
> queue support to send/receive parallel in multiple cores to speed it up ?
> Is it supported in DPDK 1.3.1r2 ?
With some cases it is possible to get multple packets per send.
This happens if rte_tx_burst is called with more than one packet.
> (C)
> There are two places using dpdk_ring_doorbell() in virtio_user.c,
> eth_tx_burst() and virtio_alloc_rxq() which is called in virtio_recv_buf().
> I looked at them further using "top perf -C 0". It could even occupies 80%
> of the logical core 0 on a CentOS 32-bit VM. Here is the implementation of
> outw() using gcc preprocessing (-E)
> static void outw(unsigned short int value, unsigned short int __port){
> __asm__ __volatile__ ("outw %w0,%w1": :"a" (value), "Nd" (__port));
> }
> Is outw command a blocking call ?
> Based on this link http://wiki.osdev.org/Inline_Assembly/Examples, I am not
> sure it is blocked/waiting.
Out word causes a VM trap back to hypervisor. Since it is not allowed
as normally by guest, and is used to notify host. Vmware uses memory
in a similar manner as a wakeup.
next prev parent reply other threads:[~2013-12-16 23:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-13 22:04 James Yu
2013-12-13 23:01 ` Stephen Hemminger
2013-12-16 23:35 ` James Yu
2013-12-16 23:58 ` Stephen Hemminger [this message]
-- strict thread matches above, loose matches on Subject: below --
2013-12-13 22:02 James Yu
2013-12-13 21:59 James Yu
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