svn commit: r352658 - head/sys/kern

[Peter Holm]

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>

- Peter