From: pintu.ping@gmail.com (Pintu Agarwal) To: kernelnewbies@lists.kernelnewbies.org Subject: [ARM64] Printing IRQ stack usage information Date: Fri, 16 Nov 2018 11:44:36 +0530 [thread overview] Message-ID: <CAOuPNLj8wj=tPJo8L3oS7o8iTQcyhZ0W-GH6xmP_GsG4r7YdAQ@mail.gmail.com> (raw) In-Reply-To: <28496.1542300549@turing-police.cc.vt.edu> On Thu, 15 Nov 2018, 10:19 pm <valdis.kletnieks@vt.edu wrote: > > On Thu, 15 Nov 2018 18:52:39 +0530, Pintu Agarwal said: > > > Currently, when I tested this (as a proc interface), I got the below output: > > CPU UNUSED-STACK ACTUAL-STACK > > 0 16368 16384 > > > 3) How should I test it to get the different usage values for unused stack ? > > Can I get these values by implementing a sample interrupt handler, > > and printing information from there? > > Hint 1: If you're in a state where seq_printf() is legal, how many IRQ's are > on this processor's IRQ stack? > > Hint 2: What are the chances that some other CPU is currently in an IRQ? > (run 'top' and look for what percent of time that's happening) > > Hint 3: what are the chances that the value of irq_stack_ptr is already stale > by the time seq_printf() finishes running? > > Hint 4: what happens to the validity of your output if you get rescheduled > in the middle of that for_each loop? > > (In other words, this code is terribly racy and is probably not going to answer > whatever debugging question you were working on.. Okay. Thanks so much for your hints. Yes, I understand that this code is horribly ugly and bad. But this is only to understand if the below logic is fine to get the irq stack usage: {{{ for_each_present_cpu(cpu) { irq_stack_ptr = IRQ_STACK_PTR(cpu); //unsigned long sp = current_stack_pointer; stack_start = (unsigned long)per_cpu(irq_stack, cpu); free_stack = irq_stack_ptr - stack_start; seq_printf(m, "%2d %10lu %10d\n", cpu, free_stack, actual); } }}} Of course, final plan is not the proc entry, but to find a relevant place to invoke it, probably during boot time, or during backtrace. > If your question is "Did one > of the CPUs blow out its IRQ stack (or come close to doing so)?" there's better > approaches. > Yes, exactly, this is what the main intention. If you have any better idea about this approach, please refer me. It will be of great help. Thank You! >
WARNING: multiple messages have this Message-ID (diff)
From: Pintu Agarwal <pintu.ping@gmail.com> To: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Cc: mark.rutland@arm.com, Jungseok Lee <jungseoklee85@gmail.com>, kernelnewbies@kernelnewbies.org, catalin.marinas@arm.com, Sungjinn Chung <barami97@gmail.com>, will.deacon@arm.com, open list <linux-kernel@vger.kernel.org>, Russell King - ARM Linux <linux@armlinux.org.uk>, Takahiro Akashi <takahiro.akashi@linaro.org>, linux-arm-kernel@lists.infradead.org Subject: Re: [ARM64] Printing IRQ stack usage information Date: Fri, 16 Nov 2018 11:44:36 +0530 [thread overview] Message-ID: <CAOuPNLj8wj=tPJo8L3oS7o8iTQcyhZ0W-GH6xmP_GsG4r7YdAQ@mail.gmail.com> (raw) Message-ID: <20181116061436.koNIPaEPXZBiOC7_qO8DTvJzaPupxe3tsPA-8vf8wCQ@z> (raw) In-Reply-To: <28496.1542300549@turing-police.cc.vt.edu> On Thu, 15 Nov 2018, 10:19 pm <valdis.kletnieks@vt.edu wrote: > > On Thu, 15 Nov 2018 18:52:39 +0530, Pintu Agarwal said: > > > Currently, when I tested this (as a proc interface), I got the below output: > > CPU UNUSED-STACK ACTUAL-STACK > > 0 16368 16384 > > > 3) How should I test it to get the different usage values for unused stack ? > > Can I get these values by implementing a sample interrupt handler, > > and printing information from there? > > Hint 1: If you're in a state where seq_printf() is legal, how many IRQ's are > on this processor's IRQ stack? > > Hint 2: What are the chances that some other CPU is currently in an IRQ? > (run 'top' and look for what percent of time that's happening) > > Hint 3: what are the chances that the value of irq_stack_ptr is already stale > by the time seq_printf() finishes running? > > Hint 4: what happens to the validity of your output if you get rescheduled > in the middle of that for_each loop? > > (In other words, this code is terribly racy and is probably not going to answer > whatever debugging question you were working on.. Okay. Thanks so much for your hints. Yes, I understand that this code is horribly ugly and bad. But this is only to understand if the below logic is fine to get the irq stack usage: {{{ for_each_present_cpu(cpu) { irq_stack_ptr = IRQ_STACK_PTR(cpu); //unsigned long sp = current_stack_pointer; stack_start = (unsigned long)per_cpu(irq_stack, cpu); free_stack = irq_stack_ptr - stack_start; seq_printf(m, "%2d %10lu %10d\n", cpu, free_stack, actual); } }}} Of course, final plan is not the proc entry, but to find a relevant place to invoke it, probably during boot time, or during backtrace. > If your question is "Did one > of the CPUs blow out its IRQ stack (or come close to doing so)?" there's better > approaches. > Yes, exactly, this is what the main intention. If you have any better idea about this approach, please refer me. It will be of great help. Thank You! > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
next prev parent reply other threads:[~2018-11-16 6:14 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-11-15 13:22 [ARM64] Printing IRQ stack usage information Pintu Agarwal 2018-11-15 13:22 ` Pintu Agarwal 2018-11-15 16:49 ` valdis.kletnieks at vt.edu 2018-11-15 16:49 ` valdis.kletnieks 2018-11-16 6:14 ` Pintu Agarwal [this message] 2018-11-16 6:14 ` Pintu Agarwal 2018-11-16 11:33 ` valdis.kletnieks at vt.edu 2018-11-16 11:33 ` valdis.kletnieks 2018-11-16 14:40 ` Pintu Agarwal 2018-11-16 14:40 ` Pintu Agarwal 2018-11-16 16:46 ` valdis.kletnieks at vt.edu 2018-11-16 16:46 ` valdis.kletnieks 2018-11-16 17:43 ` Pintu Agarwal 2018-11-16 17:43 ` Pintu Agarwal 2018-11-16 18:31 ` valdis.kletnieks at vt.edu 2018-11-16 18:31 ` valdis.kletnieks 2018-11-17 13:06 ` Pintu Agarwal 2018-11-17 13:06 ` Pintu Agarwal 2018-11-20 12:51 ` Pintu Agarwal 2018-11-20 12:51 ` Pintu Agarwal 2018-11-20 19:03 ` valdis.kletnieks at vt.edu 2018-11-20 19:03 ` valdis.kletnieks
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