[Winpcap-users] Win7 pcap_sendqueue_transmit performance

[Monroe Comstock]

GV,

The NIC Cards are the exact same (Marvell Yukon 88E8056 Gig-E), and the
motherboards are from the same manufacturer (ASUS).  They are both on the
Local Lan although there is no additional traffic since this is in my
sandbox.

Good to know about the checksum offloading.  Not a big deal. Calculating the
checksums is not a factor in my performance tests, as I am only calculating
the time it takes to call and return from the pcap_sendqueue_transmit
method.

Again, the systems are similar, but not exact matches.  They are not fresh
installs, although the WIN7 is fairly recent and is the one that is lagging.
Is there some check that can be performed to see if the protocol stack is
out of whack?

Referring to the Win7 installation, I'm curious as to why the winsock method
of sending the packets (one at a time) would be faster than using the
pcap_sendqueue_transmit.    As I mentioned, on Vista I can send the lot in
5ms using pcap_sendqueue_transmit, On Win7, winsock can do it in 15ms (one
at a time) , but pcap_sendqueue_transmit is taking upwards of 60ms.

Is there some special logging that can be turned on to try to isolate the
delay?

Greatly appreciated,

Monroe

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Today's Topics:

   1. Re: Win7 pcap_sendqueue_transmit performance (Gianluca Varenni)


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Message: 1
Date: Mon, 2 May 2011 10:58:37 -0700
From: Gianluca Varenni <Gianluca.Varenni at riverbed.com>
To: "winpcap-users at winpcap.org" <winpcap-users at winpcap.org>
Subject: Re: [Winpcap-users] Win7 pcap_sendqueue_transmit performance
Message-ID:
	<AF250ADA3E79E64A97672D195AA114E1012D122F at MAILBOXES.nbttech.com>
Content-Type: text/plain; charset="us-ascii"

Monroe,

Are you using the *same* hardware and the same network card? Also, is the
same NIC used for something else (e.g. normal LAN connection) or it's a
dedicated NIC?

The flags that you indicated are not used when sending packets out. The NIC
will *not* calculate the IP/UDP checksums for you when transmitting with
WinPcap. There is a specific negotiation process that happens between the
NIC driver and the protocol driver in order to use checksum offloading.
WinPcap does not support it.

There shouldn't be any difference if the hardware and test conditions are
the same. Also, are the two machines using a fresh, clean installation of
Win7 and Vista?

Have a nice day
GV

-----Original Message-----
From: winpcap-users-bounces at winpcap.org
[mailto:winpcap-users-bounces at winpcap.org] On Behalf Of Monroe Comstock
Sent: Monday, April 25, 2011 9:53 AM
To: winpcap-users at winpcap.org
Subject: [Winpcap-users] Win7 pcap_sendqueue_transmit performance

Hello again,

I apologize for the flurry of questions.  I'm head down developing my
application at the moment and I have run into an odd behavior that I'd like
to inquire about.

I've got an application that sends about 500 packets (about 300 bytes each)
every 10ms using the pcap_sendqueue_transmit function.  I'm also using
QueryPerformanceCounter to record the time it takes to do the send.  My
thread that sends the packets uses its own instance of a pcap_t.   I've also
tried many combinations of PCAP_OPENFLAG_MAX_RESPONSIVENESS and
PCAP_OPENFLAG_NOCAPTURE_LOCAL to see it they have any impact, yet they don't
appear to.

What I've found is that on a Vista machine (Core2 Duo 3Ghz) I can send these
packets consistently in 5ms or less.  However on a Win7 (Core i7 2.8Ghz) the
same call, using the exact same code, takes upwards of 60ms (consistently)
to send the same amount of data.  Moreover, if I disable the pcap send
functionality on the Win7 box and just use a normal winsock send, winsock
out performs pcap_sendqueue_transmit by a huge margin (about 15ms to send).
Be advised that I am NOT using time stamps and I send with "sync" set to 0.

Both machines have good NICs (GigE) with checksum offloading, although for
some reason I still seem to need to calculate the IP and UDP checksums
before I add the packets to the queue (Shouldn't the NIC card calculate
these for me?) .  But I digress...

So, my question is:  Does Windows 7 have some negative effect on the
performance of pcap_sendqueue_transmit that would cause it to have a 10 fold
increase in the transmission time?  Or have I forgotten something
elementary?

Thanks again for all your help!

Monroe


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