Benjamin LaHaise <[EMAIL PROTECTED]> writes: > Hello folks, > > 2.6.24-rc6 regresses on the 10000 network interface creation test relative to > 2.6.23. The cause appears to be the new code in sysctl_check_lookup(), which > shows up as the #1 item while profiling. Is a revert of this new code > possible until its scaling issues are fixed? 2.6.23 can do more than 100 new > network interfaces per second for the first few thousand devices, but with > 2.6.24-rc6 the results drop off rather dramatically to less than 10 interfaces > per second. The 10000 interface test is unbearable with the new sysctl_check > code.
Why do we need 10000 interfaces? Why isn't network device creation a slow path? The problem seems to be in the data structures used by sysctl. You are increasing the length of the linked list each time you add a network interface. So sysctl lookups slow down. At 10000 entries that is a long linked list walk. At 100000 things get even longer. Now the numbers you report still seem like a lot of time to me. My guess would be that we are getting badly into cache miss territory. If what you describe is a real scenario where users care we need to fix the sysctl data structures so that they scale. Because of this bug report and another one I got earlier today about a real bug in the parallel port code detected by the very lookup that is slowing you down. I am quite reluctant to contemplate pulling this code. It seems to be doing it's job, if in some cases uncomfortably so. So is this a bug report telling me that there are users with 10k or 100k interfaces that care. So we need to fix sysctl. Is there a specific kernel test case that is run often that having slow sysctl performance matters for? CONFIG_SYSCTL=n should solve that if it is specialized. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
