On Fri, Jun 16, 2017 at 02:37:40PM -0400, Chuck Lever wrote: > > > On Jun 16, 2017, at 1:52 PM, bfields@xxxxxxxxxxxx wrote: > > > > Just repeating some comments from the bug: > > > > On Fri, Jun 16, 2017 at 11:22:54AM -0400, Chuck Lever wrote: > >> Running a multi-threaded 8KB fio test (70/30 mix), three or four out > >> of twelve of the jobs fail when using krb5i. The failure is an EIO > >> on a read. > >> > >> Troubleshooting confirmed the EIO results when the client fails to > >> verify the MIC of an NFS READ reply. Bruce suggested the problem > >> could be due to the data payload changing between the time the > >> reply's MIC was computed on the server and the time the reply was > >> actually sent. > >> > >> krb5p gets around this problem by disabling RQ_SPLICE_OK. > > > > And you verified that this does fix the problem in your case. > > I've had this applied to my server for a week or so. There > hasn't been a single recurrence of the issue. > > > > So, I think it's a simple fix and probably the best we can do without a > > lot more work, so I'm happy applying it. > > > > That said, I'm still curious about the performance: > > > >> I would say that there is not much difference in this test. > > > > We added an extra copy to the read path and it didn't seem to affect > > throughput of streaming read much--I think that just says memory > > bandwidth isn't the bottlneck in this case? Which doesn't seem too > > surprising. > > With krb5i, an additional memory copy is minor compared to the > computation needed. > > I'm testing with 56Gbps networking and a tmpfs export. I'm not > exhausting the CPU on my 4-core server, even with krb5p. The > effects could be seen in a scalability test, but I don't have > anything that pushes my server that hard. > > > > I wonder what we should be looking for--maybe running the same test but > > also measuring CPU usage somehow. > > Maybe an increase in latency. But I didn't see much change, and > the throughput numbers don't reflect any underlying increase in > per-RPC latency. OK! Thanks for looking into this. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
