From: Alex Belits <abelits@marvell.com> To: "frederic@kernel.org" <frederic@kernel.org> Cc: "mingo@kernel.org" <mingo@kernel.org>, "peterz@infradead.org" <peterz@infradead.org>, "rostedt@goodmis.org" <rostedt@goodmis.org>, "Prasun Kapoor" <pkapoor@marvell.com>, "tglx@linutronix.de" <tglx@linutronix.de>, "linux-api@vger.kernel.org" <linux-api@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "catalin.marinas@arm.com" <catalin.marinas@arm.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "netdev@vger.kernel.org" <netdev@vger.kernel.org>, "davem@davemloft.net" <davem@davemloft.net>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "will@kernel.org" <will@kernel.org> Subject: Re: [EXT] Re: [PATCH 03/12] task_isolation: userspace hard isolation from kernel Date: Sun, 8 Mar 2020 06:06:19 +0000 Message-ID: <5b819b1a8c3a4c9c2361ff10a31ac91df1851b83.camel@marvell.com> (raw) In-Reply-To: <20200306152632.GB8590@lenoir> On Fri, 2020-03-06 at 16:26 +0100, Frederic Weisbecker wrote: > On Wed, Mar 04, 2020 at 04:07:12PM +0000, Alex Belits wrote: > > do { > > + /* Make sure we are reading up to date values > > */ > > + smp_mb(); > > + ind = ind_counter & 1; > > + snprintf(buf_prefix, sizeof(buf_prefix), > > + "isolation %s/%d/%d (cpu %d)", > > + desc->comm[ind], desc->tgid[ind], > > + desc->pid[ind], cpu); > > + desc->warned[ind] = true; > > + ind_counter_old = ind_counter; > > + /* Record the warned flag, then re-read > > descriptor */ > > + smp_mb(); > > + ind_counter = atomic_read(&desc->curr_index); > > + /* > > + * If the counter changed, something was > > updated, so > > + * repeat everything to get the current data > > + */ > > + } while (ind_counter != ind_counter_old); > > + } > > So the need to log the fact we are sending an event to a remote CPU > that *may be* > running an isolated task makes things very complicated and even racy. The only reason why the result of this would be wrong, is the race between multiple causes of breaking isolation of the same task or race with the task exiting isolation on its own at the same time (and possibly re-entering it, or even another task entering on the same CPU core). This is possible, however for all practical purposes we are still logging an isolation-breaking event that happened while a real isolated task was running. We should keep in mind the possibility that this isolation-breaking event could be preempted by another isolation breaking cause, and all of them will be recorded even if only one ended up causing fast_task_isolation_cpu_cleanup() to be called on the target CPU core. > How bad would it be to only log those interruptions once they land on > the target? > For the purpose of determining the cause of isolation breaking -- very bad. Early versions of this made people tear their hair out trying to divine, where some IPI came from. Then there was a monstrosity that did some rather unsafe manipulations with task_struct, however it was only suitable as a temporary mechanism for development. This version keeps things consistent and only shows up when there is something that should be reported. > Thanks. Thanks! -- Alex
next prev parent reply index Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-04 16:01 [PATCH 00/12] "Task_isolation" mode Alex Belits 2020-03-04 16:03 ` [PATCH 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits 2020-03-04 16:04 ` [PATCH 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits 2020-03-04 16:07 ` [PATCH 03/12] task_isolation: userspace hard isolation from kernel Alex Belits 2020-03-05 18:33 ` Frederic Weisbecker 2020-03-08 5:32 ` [EXT] " Alex Belits 2020-04-28 14:12 ` Marcelo Tosatti 2020-03-06 15:26 ` Frederic Weisbecker 2020-03-08 6:06 ` Alex Belits [this message] 2020-03-06 16:00 ` Frederic Weisbecker 2020-03-08 7:16 ` [EXT] " Alex Belits 2020-03-04 16:08 ` [PATCH 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits 2020-03-04 16:09 ` [PATCH 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits 2020-03-04 16:10 ` [PATCH 06/12] task_isolation: arch/arm64: " Alex Belits 2020-03-04 16:31 ` Mark Rutland 2020-03-08 4:48 ` [EXT] " Alex Belits 2020-03-04 16:11 ` [PATCH 07/12] task_isolation: arch/arm: " Alex Belits 2020-03-04 16:12 ` [PATCH 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits 2020-03-06 16:03 ` Frederic Weisbecker 2020-03-08 7:28 ` [EXT] " Alex Belits 2020-03-09 2:38 ` Frederic Weisbecker 2020-03-04 16:13 ` [PATCH 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits 2020-03-04 16:14 ` [PATCH 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits 2020-03-04 16:15 ` [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits 2020-03-06 15:34 ` Frederic Weisbecker 2020-03-08 6:48 ` [EXT] " Alex Belits 2020-03-09 2:28 ` Frederic Weisbecker 2020-03-04 16:16 ` [PATCH 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits 2020-03-08 3:42 ` [PATCH v2 00/12] "Task_isolation" mode Alex Belits 2020-03-08 3:44 ` [PATCH v2 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits 2020-03-08 3:46 ` [PATCH v2 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits 2020-03-08 3:47 ` [PATCH v2 03/12] task_isolation: userspace hard isolation from kernel Alex Belits [not found] ` <20200307214254.7a8f6c22@hermes.lan> 2020-03-08 7:33 ` [EXT] " Alex Belits 2020-03-27 8:42 ` Marta Rybczynska 2020-04-06 4:31 ` Kevyn-Alexandre Paré 2020-04-06 4:43 ` Kevyn-Alexandre Paré 2020-03-08 3:48 ` [PATCH v2 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits 2020-03-08 3:49 ` [PATCH v2 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits 2020-03-08 3:50 ` [PATCH v2 06/12] task_isolation: arch/arm64: " Alex Belits 2020-03-09 16:59 ` Mark Rutland 2020-03-08 3:52 ` [PATCH v2 07/12] task_isolation: arch/arm: " Alex Belits 2020-03-08 3:53 ` [PATCH v2 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits 2020-03-08 3:54 ` [PATCH v2 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits 2020-03-08 3:55 ` [PATCH v2 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits 2020-04-06 4:27 ` Kevyn-Alexandre Paré 2020-03-08 3:56 ` [PATCH v2 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits 2020-03-08 3:57 ` [PATCH v2 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits 2020-04-09 15:09 ` [PATCH v3 00/13] "Task_isolation" mode Alex Belits 2020-04-09 15:15 ` [PATCH 01/13] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits 2020-04-09 15:16 ` [PATCH 02/13] task_isolation: vmstat: add vmstat_idle function Alex Belits 2020-04-09 15:17 ` [PATCH v3 03/13] task_isolation: add instruction synchronization memory barrier Alex Belits 2020-04-15 12:44 ` Mark Rutland 2020-04-19 5:02 ` [EXT] " Alex Belits 2020-04-20 12:23 ` Will Deacon 2020-04-20 12:36 ` Mark Rutland 2020-04-20 13:55 ` Will Deacon 2020-04-21 7:41 ` Will Deacon 2020-04-20 12:45 ` Mark Rutland 2020-04-09 15:20 ` [PATCH v3 04/13] task_isolation: userspace hard isolation from kernel Alex Belits 2020-04-09 18:00 ` Andy Lutomirski 2020-04-19 5:07 ` Alex Belits 2020-04-09 15:21 ` [PATCH 05/13] task_isolation: Add task isolation hooks to arch-independent code Alex Belits 2020-04-09 15:22 ` [PATCH 06/13] task_isolation: arch/x86: enable task isolation functionality Alex Belits 2020-04-09 15:23 ` [PATCH v3 07/13] task_isolation: arch/arm64: " Alex Belits 2020-04-22 12:08 ` Catalin Marinas 2020-04-09 15:24 ` [PATCH v3 08/13] task_isolation: arch/arm: " Alex Belits 2020-04-09 15:25 ` [PATCH v3 09/13] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits 2020-04-09 15:26 ` [PATCH v3 10/13] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits 2020-04-09 15:27 ` [PATCH v3 11/13] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits 2020-04-09 15:27 ` [PATCH v3 12/13] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits 2020-04-09 15:28 ` [PATCH v3 13/13] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
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