On Thu, May 23, 2013 at 4:28 AM, Adam Thompson <[email protected]>wrote:
> In Henning Brauer’s recent talk at BSDCan, one of the things he alluded to > in his presentation is the bugginess of some TCP offload engines, and he > also mentioned in passing that with reasonably fast CPUs you may as well > just turn off all offloading. I've since found quite a lot of anecdotal > evidence that disabling offloading altogether actually speeds things up on > high-end servers... but very little in the way of data or guidelines. > > I wonder, do you know of any heuristics to help judge (without doing > extensive benchmarking, since I don't happen to have any Ixia gear > handy...) when we're just as well off disabling all the offload functions? > I wonder particularly about the code path to fix up tunnel packets so the > igb/em/bce/bge can do their apparently-very-special cksum offload. > > This smells to me like hardware RAID vs. software RAID, where which one is > faster (not necessarily *better*) changes depending on how fast the host > CPU is and how old the RAID card is... and it was possible, at times, to > come up with fairly accurate rules of thumb to judge when it was going to > be faster to not offload the calculations. > > And, the other relevant question is whether FreeBSD does anything more > exciting than checksum offloading? My recollection of Broadcom's version > of TCP Chimney Offloading under Windows 2008 included a bit more than just > checksums, but I don't recall the details. > > Thoughts? > > I think it all comes down to latency. If you have cpu contention and high load it would be beneficial to have the hardware(nic) do the checksum work for you anyway since the latency will be lower. > -Adam Thompson > [email protected] > > > _______________________________________________ > List mailing list > [email protected] > http://lists.pfsense.org/mailman/listinfo/list >
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