Date: Fri, 17 Feb 2012 19:28:47 +0800 From: David Xu <listlog2011@gmail.com> To: Julian Elischer <julian@freebsd.org> Cc: FreeBSD Stable <freebsd-stable@freebsd.org>, Alexander Kabaev <kan@freebsd.org>, Andriy Gapon <avg@freebsd.org>, davidxu@freebsd.org, threads@freebsd.org, Jung-uk Kim <jkim@freebsd.org> Subject: Re: pthread_cond_timedwait() broken in 9-stable? (from JAN 10) Message-ID: <4F3E39EF.3030209@gmail.com> In-Reply-To: <4F3E0A90.6080400@freebsd.org> References: <4F3C2671.3090808__7697.00510795719$1329343207$gmane$org@freebsd.org> <4F3D3E2D.9090100@FreeBSD.org> <4F3D6FDD.9050808@freebsd.org> <4F3D89CD.9050309@freebsd.org> <4F3DA27A.3090903@freebsd.org> <4F3DB3DB.2060603@gmail.com> <4F3DB91A.2090806@freebsd.org> <4F3DBE90.5030305@gmail.com> <4F3E04AB.2000508@freebsd.org> <4F3E0A90.6080400@freebsd.org>
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On 2012/2/17 16:06, Julian Elischer wrote: > On 2/16/12 11:41 PM, Julian Elischer wrote: >> adding jkim as he seems to be the last person working with TSC. >> >> >> On 2/16/12 6:42 PM, David Xu wrote: >>> On 2012/2/17 10:19, Julian Elischer wrote: >>>> On 2/16/12 5:56 PM, David Xu wrote: >>>>> On 2012/2/17 8:42, Julian Elischer wrote: >>>>>> Adding David Xu for his thoughts since he reqrote the code in >>>>>> quesiton in revision 213098 >>>>>> >>>>>> On 2/16/12 2:57 PM, Julian Elischer wrote: >>>>>>> On 2/16/12 1:06 PM, Julian Elischer wrote: >>>>>>>> On 2/16/12 9:34 AM, Andriy Gapon wrote: >>>>>>>>> on 15/02/2012 23:41 Julian Elischer said the following: >>>>>>>>>> The program fio (an IO test in ports) uses pthreads >>>>>>>>>> >>>>>>>>>> the following code (from fio-2.0.3, but its in earlier code too) >>>>>>>>>> has suddenly started misbehaving. >>>>>>>>>> >>>>>>>>>> clock_gettime(CLOCK_REALTIME,&t); >>>>>>>>>> t.tv_sec += seconds + 10; >>>>>>>>>> >>>>>>>>>> pthread_mutex_lock(&mutex->lock); >>>>>>>>>> >>>>>>>>>> while (!mutex->value&& !ret) { >>>>>>>>>> mutex->waiters++; >>>>>>>>>> ret = >>>>>>>>>> pthread_cond_timedwait(&mutex->cond,&mutex->lock,&t); >>>>>>>>>> mutex->waiters--; >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> if (!ret) { >>>>>>>>>> mutex->value--; >>>>>>>>>> pthread_mutex_unlock(&mutex->lock); >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> It turns out that 'ret' sometimes comes back instantly (on my >>>>>>>>>> machine) with a >>>>>>>>>> value of 60 (ETIMEDOUT) >>>>>>>>>> despite the fact that we set the timeout 10 seconds into the >>>>>>>>>> future. >>>>>>>>>> >>>>>>>>>> Has anyone else seen anything like this? >>>>>>>>>> (and yes the condition variable attribute have been set to >>>>>>>>>> use the REALTIME clock). >>>>>>>>> But why? >>>>>>>>> >>>>>>>>> Just a hypothesis that maybe there is some issue with time >>>>>>>>> keeping on that system. >>>>>>>>> How would that code work out for you with MONOTONIC? >>>>>>>> >>>>>>>> Jens Axboe, (CC'd) tried both CLOCK_REALTIME and >>>>>>>> CLOCK_MONOTONIC, and they both had the same problem.. >>>>>>>> i.e. random early returns with ETIMEDOUT. >>>>>>>> >>>>>>>> I think we will try move out machine forward to a newer -stable >>>>>>>> to see if it resolves. >>>>>>> Kan upgraded the machine today to today's 9.x branch tip and the >>>>>>> problem still occurs. >>>>>>> 8.x does not have this problem. >>>>>>> >>>>>>> I have not got a 9-RELEASE machine to test on.. so I can not >>>>>>> tell if this came in with the burst of stuff >>>>>>> that came in after the 9.x branch was unfrozen after the release >>>>>>> of 9.0. >>>>>>> >>>>>>> >>>>>> >>>>> I am trying to reproduce the problem, do you have complete sample >>>>> code to test ? >>>> >>>> I'm still looking the exact set >>>> but on my machine (4 cpus) the program from ports sysutils/fio >>>> exhibits the problem when used with >>>> kern.timecounter.hardware=TSC-low and with the following config file: >>>> >>>> pu05 # cat config.fio >>>> >>>> [global] >>>> #clocksource=cpu >>>> direct=1 >>>> rw=randread >>>> bs=4096 >>>> fill_device=1 >>>> numjobs=16 >>>> iodepth=16 >>>> #ioengine=posixaio >>>> #ioengine=psync >>>> ioengine=psync >>>> group_reporting >>>> norandommap >>>> time_based >>>> runtime=60000 >>>> randrepeat=0 >>>> >>>> [file1] >>>> filename=/dev/ada0 >>>> >>>> pu05 # >>>> pu05 # fio config.fio >>>> fio: this platform does not support process shared mutexes, forcing >>>> use of threads. Use the 'thread' option to get rid of this warning. >>>> file1: (g=0): rw=randread, bs=4K-4K/4K-4K, ioengine=psync, iodepth=16 >>>> ... >>>> file1: (g=0): rw=randread, bs=4K-4K/4K-4K, ioengine=psync, iodepth=16 >>>> fio 2.0.3 >>>> Starting 15 threads and 1 process >>>> fio: job startup hung? exiting. >>>> fio: 5 jobs failed to start >>>> Segmentation fault (core dumped) >>>> pu05# >>>> >>>> >>>> The reason 5 jobs failed to start is because the parent timed out >>>> on them immediately. >>>> It didn't time out on 10 of them apparently. >>>> >>>> >>>> if I set the timer to ACPI-fast it works as expected.. >>> maybe following code can check to see if TSC-LOW works by let the >>> thread run >>> on each cpu. >>> >>> gettimeofday(&prev, NULL); >>> int cpu = 0; >>> for (;;) { >>> cpuset_t set; >>> cpu = ++cpu % 4; >>> CPU_ZERO(&set); >>> CPU_SET(cpu, &set); >>> pthread_setaffinity_np(pthread_self(), sizeof(set), &set); >>> gettimeofday(&cur, NULL); >>> if ( timercmp(&prev, &cur, >=)) { >>> abort(); >>> } >>> } >>> >>> > > pu05# sysctl kern.timecounter.hardware=TSC-low > kern.timecounter.hardware: ACPI-fast -> TSC-low > pu05# ./test > ^C > pu05# cat test.c > > #include <stdlib.h> > #include <sys/param.h> > #include <sys/cpuset.h> > #include <pthread_np.h> > > #include <sys/time.h> > > main() > { > int cpu = 0; > struct timeval prev, cur; > > gettimeofday(&prev, NULL); > for (;;) { > cpuset_t set; > cpu = ++cpu % 4; > CPU_ZERO(&set); > CPU_SET(cpu, &set); > pthread_setaffinity_np(pthread_self(), sizeof(set), &set); > gettimeofday(&cur, NULL); > if ( timercmp(&prev, &cur, >)) { > abort(); > } > prev = cur; > } > } > > pu05# ./test > > minutes pass....... > > ^C > pu05# > > so it looks as if the TSC is working ok.. > I'm just going to check that the program is actually moving CPU... > yes it is moving around but I can't tell at what speed. (according to > top). > > so we are still left with a question of "where is the problem?" > > kernel TSC driver? > generic gettimeofday() code? > pthreads cond code? > the application? > > I am running the fio test on my notebook which is using TSC-low, it is on 9.0-RC3, I can not reproduce the problem for minutes, then I interrupt it with ctrl-c: http://people.freebsd.org/~davidxu/tsc_pthread/dmesg.txt http://people.freebsd.org/~davidxu/tsc_pthread/tc.txt http://people.freebsd.org/~davidxu/tsc_pthread/fio.txt
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