Date: Wed, 21 Sep 2016 09:11:24 +0200 From: Julien Charbon <jch@freebsd.org> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-stable@FreeBSD.org, hiren panchasara <hiren@strugglingcoder.info> Subject: Re: 11.0 stuck on high network load Message-ID: <f644cd52-4377-aa90-123a-3a2887972bbc@freebsd.org> In-Reply-To: <20160920202633.GQ2840@zxy.spb.ru> References: <20160905014612.GA42393@strugglingcoder.info> <20160914213503.GJ2840@zxy.spb.ru> <20160915085938.GN38409@kib.kiev.ua> <20160915090633.GS2840@zxy.spb.ru> <20160916181839.GC2960@zxy.spb.ru> <20160916183053.GL9397@strugglingcoder.info> <20160916190330.GG2840@zxy.spb.ru> <78cbcdc9-f565-1046-c157-2ddd8fcccc62@freebsd.org> <20160919204328.GN2840@zxy.spb.ru> <8ba75d6e-4f01-895e-0aed-53c6c6692cb9@freebsd.org> <20160920202633.GQ2840@zxy.spb.ru>
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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 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. >> #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. 51.86% [2413083] lock_delay @ /boot/kernel.VSTREAM/kernel 100.0% [2413083] __rw_wlock_hard 100.0% [2413083] tcp_tw_2msl_scan -- Julien
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