Messages in this thread | | | From | "gis88530" <> | Subject | Re: skbuff.h | Date | Mon, 9 Apr 2001 23:46:58 +0800 |
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Thanks a lot. Do you know the purpose of csum_partial( ) function? I can't find out it source code.
I can't believe that I have discovered an area where an improvement in performance. Maybe I loss some thing.
Cheers, Tom
> On Mon, 9 Apr 2001, nctucis wrote: > > > Hi, > > > > I use 2.2.16 kernel. > > I found that there is a sk_buff structure in > > "/usr/src/linux/include/linux/skbuff.c", and > > there is a variable "unsigned in csum;" in > > the sk_buff structure. > > > > I want to know this checksum check what information. > > Could you give me a hand, please? > > > > -=-=-=-=-=-=-=- > > In fact, I found 64byte and 1518byte UDP packet waste different > > time to do masquerade(ip_fw_masquerade). > > Many books say NAT just modify header fields, so it should no > > different between small and big packet size. > > I guess the different time due to csum_partial(h.raw, doff, sum) > > in ip_fw_masquerade(). Right? Thanks a lot. > > (But I can't find out source code of this function.) > > > > Cheers, > > Tom > > TCP/IP packets contain a checksum. The checksum is defined by the > standards. Linux checksums the IP packets in two ways, the first > is obvious, the second is the 'csum_partial_copy_generic' in > ../linux/arch/i386/lib/checksum.S. > > NAT, because it modifies the IP packet, must also modify the > checksum. However, the checksum is in the IP header so your > 'books' are correct. FYI, since the checksum is known, the > IP address is known, and the standard is known. It is not > necessary to re-checksum the entire packet to produce a new > checksum after modification of some of the checksummed data > (IP address). > > I think Linux recalculates the entire checksum over again so > you may have discovered an area where an improvement in performance > could be obtained. > > > Cheers, > Dick Johnson > > Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips). > > "Memory is like gasoline. You use it up when you are running. Of > course you get it all back when you reboot..."; Actual explanation > obtained from the Micro$oft help desk. > > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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