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[2.7.225.93]) by smtp.gmail.com with ESMTPSA id n4-20020a1ca404000000b003973b9d0447sm175451wme.36.2022.05.30.12.35.06 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 May 2022 12:35:06 -0700 (PDT) Message-ID: Date: Mon, 30 May 2022 21:35:05 +0200 List-Id: Technical discussions relating to FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-hackers List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-hackers@freebsd.org MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: Hang ast / pipelk / piperd Content-Language: en-US To: FreeBSD Hackers References: <84015bf9-8504-1c3c-0ba5-58d0d7824843@gmail.com> From: Paul Floyd In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4LBlx80jhVz3R50 X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20210112 header.b="FZt3GEI/"; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (mx1.freebsd.org: domain of paulf2718@gmail.com designates 2a00:1450:4864:20::431 as permitted sender) smtp.mailfrom=paulf2718@gmail.com X-Spamd-Result: default: False [-2.41 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_SPF_ALLOW(-0.20)[+ip6:2a00:1450:4000::/36:c]; FREEMAIL_FROM(0.00)[gmail.com]; RCVD_COUNT_THREE(0.00)[3]; TO_DN_ALL(0.00)[]; DKIM_TRACE(0.00)[gmail.com:+]; DMARC_POLICY_ALLOW(-0.50)[gmail.com,none]; RECEIVED_SPAMHAUS_PBL(0.00)[2.7.225.93:received]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2a00:1450::/32, country:US]; MID_RHS_MATCH_FROM(0.00)[]; DWL_DNSWL_NONE(0.00)[gmail.com:dkim]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20210112]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-hackers@freebsd.org]; RCPT_COUNT_ONE(0.00)[1]; NEURAL_SPAM_SHORT(0.59)[0.591]; RCVD_IN_DNSWL_NONE(0.00)[2a00:1450:4864:20::431:from]; MLMMJ_DEST(0.00)[freebsd-hackers]; RCVD_TLS_ALL(0.00)[] X-ThisMailContainsUnwantedMimeParts: N On 5/30/22 14:15, Mark Johnston wrote: > "procstat -kk " 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 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