From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5140079D8 for ; Mon, 5 Feb 2024 01:27:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.112 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707096474; cv=none; b=lsvCl8aPYvS+2boOqKm09zCemRq1LORLwwLE3SLoVaI0btYJAtjjpXhMsOHg0sFyxmx998azbwyesd+MckjI08ZuBlnz0mGh5y1IwUFeYCTX1Chah0RLHU4vsTTSNtn3YbCU7Uxc2giZiy2FXL5QYUpbCFFswLyPHjzqsKw5vCY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707096474; c=relaxed/simple; bh=RZuaIIPKo1gIRX3J6YMBdAg3JwU1iHhJyCTVK014UoM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kNkqf7h4YSlzJ+udFSP4Wx5pOEydxwPx2yWGqAyobCLFat4P0vRHrucx1sVjQGtorfCn8Bj7mdLEF+s6MNI2DSYYVvKLEV5XQPZVCJbXFEDOt/kNKmSCuwVdeUogoN7t6LvsqFZ/mkuM+3u7X1XZ6k7itj//gbovKaioHF8WMu8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=hkOK18Iu; arc=none smtp.client-ip=115.124.30.112 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="hkOK18Iu" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1707096463; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=82lx0V+r+hq4gJMAawllOmoEwAaC/Xu93UlLHA5IJyc=; b=hkOK18IuDssqZeDWZO2JpEZTxq8HaZy+4FohOPMJ9xe64QV4RwqoXrJ7nMf3yOxiRz3FtW7/jmN1VwdiQVSxDEUDoPKFdbMIE7yFu9wbgBdqqVDiMUzK5y1RP5a4YsnzUPJa3/kV8fFhgN6NCaNAvzn8gBLT2tODK29U8KyFBDQ= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R401e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=liusong@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0W01zmjj_1707096461; Received: from 30.178.80.101(mailfrom:liusong@linux.alibaba.com fp:SMTPD_---0W01zmjj_1707096461) by smtp.aliyun-inc.com; Mon, 05 Feb 2024 09:27:42 +0800 Message-ID: Date: Mon, 5 Feb 2024 09:27:39 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv4 1/3] watchdog/softlockup: low-overhead detection of interrupt To: Bitao Hu , dianders@chromium.org, akpm@linux-foundation.org, pmladek@suse.com, kernelfans@gmail.com Cc: linux-kernel@vger.kernel.org References: <20240204145154.11069-1-yaoma@linux.alibaba.com> <20240204145154.11069-2-yaoma@linux.alibaba.com> From: Liu Song In-Reply-To: <20240204145154.11069-2-yaoma@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2024/2/4 22:51, Bitao Hu 写道: > The following softlockup is caused by interrupt storm, but it cannot be > identified from the call tree. Because the call tree is just a snapshot > and doesn't fully capture the behavior of the CPU during the soft lockup. > watchdog: BUG: soft lockup - CPU#28 stuck for 23s! [fio:83921] > ... > Call trace: > __do_softirq+0xa0/0x37c > __irq_exit_rcu+0x108/0x140 > irq_exit+0x14/0x20 > __handle_domain_irq+0x84/0xe0 > gic_handle_irq+0x80/0x108 > el0_irq_naked+0x50/0x58 > > Therefore，I think it is necessary to report CPU utilization during the > softlockup_thresh period (report once every sample_period, for a total > of 5 reportings), like this: > watchdog: BUG: soft lockup - CPU#28 stuck for 23s! [fio:83921] > CPU#28 Utilization every 4s during lockup: > #1: 0% system, 0% softirq, 100% hardirq, 0% idle > #2: 0% system, 0% softirq, 100% hardirq, 0% idle > #3: 0% system, 0% softirq, 100% hardirq, 0% idle > #4: 0% system, 0% softirq, 100% hardirq, 0% idle > #5: 0% system, 0% softirq, 100% hardirq, 0% idle > ... > > This would be helpful in determining whether an interrupt storm has > occurred or in identifying the cause of the softlockup. The criteria for > determination are as follows: > a. If the hardirq utilization is high, then interrupt storm should be > considered and the root cause cannot be determined from the call tree. > b. If the softirq utilization is high, then we could analyze the call > tree but it may cannot reflect the root cause. > c. If the system utilization is high, then we could analyze the root > cause from the call tree. > > Signed-off-by: Bitao Hu > --- > kernel/watchdog.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 91 insertions(+) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 81a8862295d6..7b121e166b81 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -16,6 +16,8 @@ > #include > #include > #include > +#include > +#include > #include > #include > #include > @@ -333,6 +335,92 @@ __setup("watchdog_thresh=", watchdog_thresh_setup); > > static void __lockup_detector_cleanup(void); > > +#ifdef CONFIG_IRQ_TIME_ACCOUNTING > +#define NUM_STATS_GROUPS 5 > +enum stats_per_group { > + STATS_SYSTEM, > + STATS_SOFTIRQ, > + STATS_HARDIRQ, > + STATS_IDLE, > + NUM_STATS_PER_GROUP, > +}; > +static const enum cpu_usage_stat tracked_stats[NUM_STATS_PER_GROUP] = { > + CPUTIME_SYSTEM, > + CPUTIME_SOFTIRQ, > + CPUTIME_IRQ, > + CPUTIME_IDLE, > +}; > +static DEFINE_PER_CPU(u16, cpustat_old[NUM_STATS_PER_GROUP]); > +static DEFINE_PER_CPU(u8, cpustat_util[NUM_STATS_GROUPS][NUM_STATS_PER_GROUP]); > +static DEFINE_PER_CPU(u8, cpustat_tail); > + > +/* > + * We don't need nanosecond resolution. A granularity of 16ms is > + * sufficient for our precision, allowing us to use u16 to store > + * cpustats, which will roll over roughly every ~1000 seconds. > + * 2^24 ~= 16 * 10^6 > + */ > +static u16 get_16bit_precision(u64 data_ns) > +{ > + return data_ns >> 24LL; /* 2^24ns ~= 16.8ms */ > +} > + > +static void update_cpustat(void) > +{ > + int i; > + u8 util; > + u16 old_stat; > + u16 new_stat; > + u8 tail = __this_cpu_read(cpustat_tail); > + struct kernel_cpustat kcpustat; > + u64 *cpustat = kcpustat.cpustat; > + u16 sample_period_16 = get_16bit_precision(sample_period); > + > + kcpustat_cpu_fetch(&kcpustat, smp_processor_id()); > + for (i = 0; i < NUM_STATS_PER_GROUP; i++) { > + old_stat = __this_cpu_read(cpustat_old[i]); > + new_stat = get_16bit_precision(cpustat[tracked_stats[i]]); > + util = DIV_ROUND_UP(100 * (new_stat - old_stat), sample_period_16); > + __this_cpu_write(cpustat_util[tail][i], util); > + __this_cpu_write(cpustat_old[i], new_stat); > + } > + __this_cpu_write(cpustat_tail, (tail + 1) % NUM_STATS_GROUPS); > +} > + > +static void print_cpustat(void) > +{ > + int i; > + int group; > + u8 tail = __this_cpu_read(cpustat_tail); > + u64 sample_period_second = sample_period; > + > + do_div(sample_period_second, NSEC_PER_SEC); > + /* > + * We do not want the "watchdog: " prefix on every line, > + * hence we use "printk" instead of "pr_crit". > + */ > + printk(KERN_CRIT "CPU#%d Utilization every %llus during lockup:\n", > + smp_processor_id(), sample_period_second); > + for (i = 0; i < NUM_STATS_GROUPS; i++) { > + group = (tail + i) % NUM_STATS_GROUPS; > + printk(KERN_CRIT "\t#%d: %3u%% system,\t%3u%% softirq,\t" > + "%3u%% hardirq,\t%3u%% idle\n", i+1, > + __this_cpu_read(cpustat_util[group][STATS_SYSTEM]), > + __this_cpu_read(cpustat_util[group][STATS_SOFTIRQ]), > + __this_cpu_read(cpustat_util[group][STATS_HARDIRQ]), > + __this_cpu_read(cpustat_util[group][STATS_IDLE])); > + } > +} > + > +static void report_cpu_status(void) > +{ > + print_cpustat(); > +} > +#else > +static inline void update_cpustat(void) { } > +static inline void report_cpu_status(void) { } > +#endif > + > /* > * Hard-lockup warnings should be triggered after just a few seconds. Soft- > * lockups can have false positives under extreme conditions. So we generally > @@ -504,6 +592,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > */ > period_ts = READ_ONCE(*this_cpu_ptr(&watchdog_report_ts)); > > + update_cpustat(); > + > /* Reset the interval when touched by known problematic code. */ > if (period_ts == SOFTLOCKUP_DELAY_REPORT) { > if (unlikely(__this_cpu_read(softlockup_touch_sync))) { > @@ -539,6 +629,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", > smp_processor_id(), duration, > current->comm, task_pid_nr(current)); > + report_cpu_status(); > print_modules(); > print_irqtrace_events(current); > if (regs) Looks good, and advisable to combine declarations of variables of the same type into one line to save on the number of lines. Reviewed-by: Liu Song