Date: Mon, 30 May 2022 21:35:05 +0200 From: Paul Floyd <paulf2718@gmail.com> To: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: Hang ast / pipelk / piperd Message-ID: <b598c89e-f11a-eed1-3d74-c3ef37bc400a@gmail.com> In-Reply-To: <YpTRj7jVE0jfbxPO@nuc> References: <84015bf9-8504-1c3c-0ba5-58d0d7824843@gmail.com> <dca6a5b4-6f0c-98c0-2f2d-6e5da7405af4@gmail.com> <YpTRj7jVE0jfbxPO@nuc>
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On 5/30/22 14:15, Mark Johnston wrote:
> "procstat -kk <valgrind PID>" might help to reveal what's going on,
> since it sounds like the hand/livelock is happening somewhere in the
> kernel.
Not knowing much about the kernel, my guess is that this is related to
commit 4808bab7fa6c3ec49b49476b8326d7a0250a03fa
Author: Alexander Motin <mav@FreeBSD.org>
Date: Tue Sep 21 18:14:22 2021 -0400
sched_ule(4): Improve long-term load balancer.
and this bit of ast code
doreti_ast:
/*
* Check for ASTs atomically with returning. Disabling CPU
* interrupts provides sufficient locking even in the SMP case,
* since we will be informed of any new ASTs by an IPI.
*/
cli
movq PCPU(CURTHREAD),%rax
testl $TDF_ASTPENDING | TDF_NEEDRESCHED,TD_FLAGS(%rax)
je doreti_exit
sti
movq %rsp,%rdi /* pass a pointer to the trapframe */
call ast
jmp doreti_ast
The above commit seems to be migrating loaded threads to another CPU.
My test system is a VirtualBox amd64 FreeBSD 13.1 with one CPU running
on a 13.0 host.
I just tried restarting the VM with 2 CPUs and the testcase seems to be
a lot better - it's been running in a loop for 10 minutes whereas
previously it would hang at least 1 in 5 times.
A+
Paul
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