On Wed, Sep 21, 2016 at 09:11:24AM +0200, Julien Charbon wrote: > > Hi Slawa, > > On 9/20/16 10:26 PM, Slawa Olhovchenkov wrote: > > On Tue, Sep 20, 2016 at 10:00:25PM +0200, Julien Charbon wrote: > >> On 9/19/16 10:43 PM, Slawa Olhovchenkov wrote: > >>> On Mon, Sep 19, 2016 at 10:32:13PM +0200, Julien Charbon wrote: > >>>> > >>>>> @ CPU_CLK_UNHALTED_CORE [4653445 samples] > >>>>> > >>>>> 51.86% [2413083] lock_delay @ /boot/kernel.VSTREAM/kernel > >>>>> 100.0% [2413083] __rw_wlock_hard > >>>>> 100.0% [2413083] tcp_tw_2msl_scan > >>>>> 99.99% [2412958] pfslowtimo > >>>>> 100.0% [2412958] softclock_call_cc > >>>>> 100.0% [2412958] softclock > >>>>> 100.0% [2412958] intr_event_execute_handlers > >>>>> 100.0% [2412958] ithread_loop > >>>>> 100.0% [2412958] fork_exit > >>>>> 00.01% [125] tcp_twstart > >>>>> 100.0% [125] tcp_do_segment > >>>>> 100.0% [125] tcp_input > >>>>> 100.0% [125] ip_input > >>>>> 100.0% [125] swi_net > >>>>> 100.0% [125] intr_event_execute_handlers > >>>>> 100.0% [125] ithread_loop > >>>>> 100.0% [125] fork_exit > >>>> > >>>> The only write lock tcp_tw_2msl_scan() tries to get is a > >>>> INP_WLOCK(inp). Thus here, tcp_tw_2msl_scan() seems to be stuck > >>>> spinning on INP_WLOCK (or pfslowtimo() is going crazy and calls > >>>> tcp_tw_2msl_scan() at high rate but this will be quite unexpected). > >>>> > >>>> Thus my hypothesis is that something is holding the INP_WLOCK and not > >>>> releasing it, and tcp_tw_2msl_scan() is spinning on it. > >>>> > >>>> If you can, could you compile the kernel with below options: > >>>> > >>>> options DDB # Support DDB. > >>>> options DEADLKRES # Enable the deadlock resolver > >>>> options INVARIANTS # Enable calls of extra sanity > >>>> checking > >>>> options INVARIANT_SUPPORT # Extra sanity checks of internal > >>>> structures, required by INVARIANTS > >>>> options WITNESS # Enable checks to detect > >>>> deadlocks and cycles > >>>> options WITNESS_SKIPSPIN # Don't run witness on spinlocks > >>>> for speed > >>> > >>> Currently this host run with 100% CPU load (on all cores), i.e. > >>> enabling WITNESS will be significant drop performance. > >>> Can I use only some subset of options? > >>> > >>> Also, I can some troubles to DDB enter in this case. > >>> May be kgdb will be success (not tryed yet)? > >> > >> If these kernel options will certainly slow down your kernel, they also > >> might found the root cause of your issue before reaching the point where > >> you have 100% cpu load on all cores (thanks to INVARIANTS). I would > >> suggest: > > > > Hmmm, may be I am not clarified. > > This host run at peak hours with 100% CPU load as normal operation, > > this is for servering 2x10G, this is CPU load not result of lock > > issuse, this is not us case. And this is because I am fear to enable > > WITNESS -- I am fear drop performance. > > > > This lock issuse happen irregulary and may be caused by other issuse > > (nginx crashed). In this case about 1/3 cores have 100% cpu load, > > perhaps by this lock -- I am can trace only from one core and need > > more then hour for this (may be on other cores different trace, I > > can't guaranted anything). > > I see, especially if you are running in production WITNESS might indeed > be not practical for you. In this case, I would suggest before doing > WITNESS and still get more information to: > > #0: Do a lock profiling: > > https://www.freebsd.org/cgi/man.cgi?query=LOCK_PROFILING > > options LOCK_PROFILING > > Example of usage: > > # Run > $ sudo sysctl debug.lock.prof.enable=1 > $ sleep 10 > $ sudo sysctl debug.lock.prof.enable=0 > > # Get results > $ sysctl debug.lock.prof.stats | head -2; sysctl debug.lock.prof.stats | > sort -n -k 4 -r
OK, but in case of leak lock (why inp lock too long for tcp_tw_2msl_scan?) I can't see cause of this lock running this commands after stuck happen? > You can also use Dtrace and lockstat (especially with the lockstat -s > option): > > https://wiki.freebsd.org/DTrace/One-Liners#Kernel_Locks > https://www.freebsd.org/cgi/man.cgi?query=lockstat&manpath=FreeBSD+11.0-RELEASE > > But I am less familiar with Dtrace/lockstat tools. OK, interesting too. Thanks. > >> #1. Try above kernel options at least once, and see what you can get. > > > > OK, I am try this after some time. > > > >> #2. If #1 is a total failure try below patch: It won't solve anything, > >> it just makes tcp_tw_2msl_scan() less greedy when there is contention on > >> the INP write lock. If it makes the debugging more feasible, continue > >> to #3. > > > > OK, thanks. > > What purpose to not skip locked tcptw in this loop? > > If I understand your question correctly: According to your pmcstat > result, tcp_tw_2msl_scan() currently struggles with a write lock > (__rw_wlock_hard) and the only write lock used tcp_tw_2msl_scan() is > INP_WLOCK. No sign of contention on TW_RLOCK(V_tw_lock) currently. As I see in code, tcp_tw_2msl_scan got first node from V_twq_2msl and need got RW lock on inp w/o alternates. Can tcp_tw_2msl_scan skip current node and go to next node in V_twq_2msl list if current node locked by some reasson? > 51.86% [2413083] lock_delay @ /boot/kernel.VSTREAM/kernel > 100.0% [2413083] __rw_wlock_hard > 100.0% [2413083] tcp_tw_2msl_scan > > -- > Julien _______________________________________________ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
