tcpdump mailing list archives
Re: packet drops and zero copy filtering?
From: Richard Sharpe <rsharpe () richardsharpe com>
Date: Sun, 13 Jul 2003 22:17:29 -0700 (PDT)
On Sun, 13 Jul 2003, Ben Greear wrote:
Guy Harris wrote:On Sun, Jul 13, 2003 at 03:32:56PM -0700, Yuchung Cheng wrote:I also run tcpdump on a busy gigabites link (90MBps) and tcpdump is dropping lots of packets and locking up the cpu, is there any patch for using Linux sendfile(2) to minimize dumping to file overhead for capturing?Well, that might be an interesting patch, but it wouldn't write out a tcpdump-format file, it'd write out a Linux-format file (and given that at least some of the information in the packet header isn't returned by "recvfrom()" in the buffer, it's returned from elsewhere, it might not even be possible without a *kernel* patch as well).Seems you cannot use sendfile when reading from a socket, so can't capture like this. It will definately need a kernel module.
Well, the first poster's question does not make any sense, but it does not seem to me that the claim that you can't use sendfile when reading from a socket makes any sense either. I thought Linux's sendfile was symmetric in that regard, unlike, say, sendfile under FreeBSD, where you cannot use sendfile to read from a socket. It seems to me that the real problem is that sendfile is designed to copy to/from a socket and a file while in kernel-space to avoid the overhead of copying the data out to user-space and back again. I don't think that with packet filtering you really have a socket, although I could be wrong on that score. Regards ----- Richard Sharpe, rsharpe[at]ns.aus.com, rsharpe[at]samba.org, sharpe[at]ethereal.com, http://www.richardsharpe.com - This is the TCPDUMP workers list. It is archived at http://www.tcpdump.org/lists/workers/index.html To unsubscribe use mailto:tcpdump-workers-request () tcpdump org?body=unsubscribe
Current thread:
- packet drops and zero copy filtering? Yuchung Cheng (Jul 13)
- Re: packet drops and zero copy filtering? Guy Harris (Jul 13)
- Re: packet drops and zero copy filtering? Ben Greear (Jul 13)
- Re: packet drops and zero copy filtering? Richard Sharpe (Jul 13)
- Re: packet drops and zero copy filtering? Ben Greear (Jul 14)
- Re: packet drops and zero copy filtering? Richard Sharpe (Jul 14)
- Re: packet drops and zero copy filtering? Guy Harris (Jul 14)
- Re: packet drops and zero copy filtering? Loris Degioanni (Jul 14)
- Re: packet drops and zero copy filtering? Ben Greear (Jul 13)
- Re: packet drops and zero copy filtering? Guy Harris (Jul 14)
- Re: packet drops and zero copy filtering? Guy Harris (Jul 13)