svn commit: r352658 - head/sys/kern

[Michael Tuexen]

> On 25. Sep 2019, at 07:13, Peter Holm <pho at FreeBSD.org> wrote:
> 
> On Tue, Sep 24, 2019 at 08:01:20PM +0000, Alexander Motin wrote:
>> Author: mav
>> Date: Tue Sep 24 20:01:20 2019
>> New Revision: 352658
>> URL: https://svnweb.freebsd.org/changeset/base/352658
>> 
>> Log:
>>  Fix/improve interrupt threads scheduling.
>> 
>>  Doing some tests with very high interrupt rates I've noticed that one of
>>  conditions I added in r232207 to make interrupt threads in most cases
>>  run on local CPU never worked as expected (worked only if previous time
>>  it was executed on some other CPU, that is quite opposite).  It caused
>>  additional CPU usage to run full CPU search and could schedule interrupt
>>  threads to some other CPU.
>> 
>>  This patch removes that code and instead reuses existing non-interrupt
>>  code path with some tweaks for interrupt case:
>>   - On SMT systems, if current thread is idle, don't look on other threads.
>>  Even if they are busy, it may take more time to do fill search and bounce
>>  the interrupt thread to other core then execute it locally, even sharing
>>  CPU resources.  It is other threads should migrate, not bound interrupts.
>>   - Try hard to keep interrupt threads within LLC of their original CPU.
>>  This improves scheduling cost and supposedly cache and memory locality.
>> 
>>  On a test system with 72 threads doing 2.2M IOPS to NVMe this saves few
>>  percents of CPU time while adding few percents to IOPS.
>> 
>>  MFC after:	1 month
>>  Sponsored by:	iXsystems, Inc.
>> 
>> Modified:
>>  head/sys/kern/sched_ule.c
>> 
>> Modified: head/sys/kern/sched_ule.c
>> ==============================================================================
>> --- head/sys/kern/sched_ule.c	Tue Sep 24 18:18:11 2019	(r352657)
>> +++ head/sys/kern/sched_ule.c	Tue Sep 24 20:01:20 2019	(r352658)
>> @@ -1251,7 +1251,7 @@ sched_pickcpu(struct thread *td, int flags)
> 
> Could this be yours?
> 
> FreeBSD/SMP: Multiprocessor System Detected: 24 CPUs
> FreeBSD/SMP: 2 package(s) x 6 core(s) x 2 hardware threads
> random: unblocking device.
> Firmware Warning (ACPI): Invalid length for FADT/Pm1aControlBlock: 32, using default 16 (20190703/tbfadt-850)
> ioapic0 <Version 2.0> irqs 0-23
> ioapic1 <Version 2.0> irqs 24-47
> ioapic2 <Version 2.0> irqs 48-71
> Launching APs: 13 6 18 17 5 9 8 19 7 10 1 11 2 12 14 15 20 4 21 16 22 3 23
> panic: sched_pickcpu: Failed to find a cpu.
> cpuid = 0
> time = 1
> KDB: stack backtrace:
> db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xffffffff8254a830
> vpanic() at vpanic+0x19d/frame 0xffffffff8254a880
> panic() at panic+0x43/frame 0xffffffff8254a8e0
> sched_pickcpu() at sched_pickcpu+0x4c1/frame 0xffffffff8254a990
> sched_add() at sched_add+0x6e/frame 0xffffffff8254a9d0
> gtaskqueue_start_threads() at gtaskqueue_start_threads+0x124/frame 0xffffffff8254aa70
> taskqgroup_cpu_create() at taskqgroup_cpu_create+0x135/frame 0xffffffff8254aab0
> taskqgroup_adjust() at taskqgroup_adjust+0x1ad/frame 0xffffffff8254ab20
> mi_startup() at mi_startup+0x210/frame 0xffffffff8254ab70
> btext() at btext+0x2c
> KDB: enter: panic
> [ thread pid 0 tid 100000 ]
> Stopped at      kdb_enter+0x3b: movq    $0,kdb_why
> db>
Also triggered by syzkaller:
https://syzkaller.appspot.com/bug?id=27e65a528a1431f0aeea7b7814e685bddf769747

Best regards
Michael
> 
> - Peter

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 5257 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/svn-src-all/attachments/20190925/5ecbc68a/attachment.bin>