From owner-svn-src-all@freebsd.org Tue Jun 5 10:21:56 2018 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 852D3FE24EB; Tue, 5 Jun 2018 10:21:56 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id E59076E6D8; Tue, 5 Jun 2018 10:21:55 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTP id w55ALj4V049691; Tue, 5 Jun 2018 13:21:48 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua w55ALj4V049691 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id w55ALiuU049690; Tue, 5 Jun 2018 13:21:44 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 5 Jun 2018 13:21:44 +0300 From: Konstantin Belousov To: Matthew Macy Cc: src-committers , svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r334595 - in head: sys/dev/hwpmc sys/kern sys/sys usr.sbin/pmcstat Message-ID: <20180605102144.GF2450@kib.kiev.ua> References: <201806040110.w541ANZr044727@repo.freebsd.org> <20180604120815.GB2450@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Jun 2018 10:21:56 -0000 On Mon, Jun 04, 2018 at 10:27:21AM -0700, Matthew Macy wrote: > On Mon, Jun 4, 2018 at 5:08 AM, Konstantin Belousov wrote: > > On Mon, Jun 04, 2018 at 01:10:23AM +0000, Matt Macy wrote: > >> @@ -2214,6 +2236,11 @@ pmc_hook_handler(struct thread *td, int function, void > >> > >> pmc_capture_user_callchain(PCPU_GET(cpuid), PMC_HR, > >> (struct trapframe *) arg); > >> + > >> + KASSERT(td->td_pinned == 1, > >> + ("[pmc,%d] invalid td_pinned value", __LINE__)); > >> + sched_unpin(); /* Can migrate safely now. */ > > sched_pin() is called from pmc_post_callchain_callback(), which is > > called from userret(). userret() is executed with interrupts and > > preemption enabled, so there is a non-trivial chance that the thread > > already migrated. > > > > In fact, I do not see a need to disable migration for the thread if user > > callchain is planned to be gathered. You only need to remember the cpu > > where the interrupt occured, to match it against the request. Or are > > per-cpu PMC registers still accessed during callchain collection ? > > The buffers are pcpu. Although it would in principle be safe in this > case since I > don't modify the read/write indices. However, I'd have to add another field for > the CPU and it doesn't handle the case of multiple migrations. > You already moved the collection to userret(), thanks. So the only reason to sched_pin() in pmc_process_thread_userret() is to make pmc_capture_user_callchain() to operate on the stable cpu ? May be, add a comment there, and move the assert that td_pinned > 0, into pmc_capture_user_callchain() ? > > > >> +int > >> +pmc_process_interrupt(int cpu, int ring, struct pmc *pm, struct trapframe *tf, > >> + int inuserspace) > >> +{ > >> + struct thread *td; > >> + > >> + td = curthread; > >> + if ((pm->pm_flags & PMC_F_USERCALLCHAIN) && > >> + td && td->td_proc && > >> + (td->td_proc->p_flag & P_KPROC) == 0 && > >> + !inuserspace) { > > I am curious why a lot of the pmc code checks for curthread != NULL and, > > like this fragment, for curproc != NULL. I am sure that at least on x86, > > we never let curthread point to the garbage, even during the context > > switches. NMI handler has the same cargo-cult check, BTW. > > I didn't think they could be NULL, but have been cargo culting the > existing code. You already cleaned this, thanks. > > > Also, please fix the indentation of the conditions block. > > > > > >> + atomic_add_int(&curthread->td_pmcpend, 1); > > You can use atomic_store_int() there, I believe, Then there would be > > no locked op executed at all, on x86. > > Storing a 1 would enable me to early terminate the loop. > > > > >> @@ -375,6 +375,7 @@ struct thread { > >> void *td_lkpi_task; /* LinuxKPI task struct pointer */ > >> TAILQ_ENTRY(thread) td_epochq; /* (t) Epoch queue. */ > >> epoch_section_t td_epoch_section; /* (t) epoch section object */ > >> + int td_pmcpend; > > Why this member was not put into the zeroed region ? Wouldn't a garbage > > there cause uneccessary ASTs ? > > It would cause _1_ unnecessary check for callchains after initial > creation. Putting it in the zero area would break the ABI. We do not care about KBI stability on HEAD. If you care about it more than usual, you can bump __FreeBSD_version to prevent older modules from load, when struct thread layout changed. Practically we change KBI as needed without special measures.