From: Peter Zijlstra <peterz@infradead.org>
To: Josh Don <joshdon@google.com>
Cc: Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] cgroup: add cpu.stat_percpu
Date: Tue, 11 Jan 2022 13:49:59 +0100 [thread overview]
Message-ID: <Yd189wHB2LJcK1Pv@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20220107234138.1765668-1-joshdon@google.com>
On Fri, Jan 07, 2022 at 03:41:37PM -0800, Josh Don wrote:
> + seq_puts(seq, "usage_usec");
> + for_each_possible_cpu(cpu) {
> + cached_bstat = per_cpu_ptr(&cached_percpu_stats, cpu);
> + val = cached_bstat->cputime.sum_exec_runtime;
> + do_div(val, NSEC_PER_USEC);
> + seq_printf(seq, " %llu", val);
> + }
> + seq_puts(seq, "\n");
> +
> + seq_puts(seq, "user_usec");
> + for_each_possible_cpu(cpu) {
> + cached_bstat = per_cpu_ptr(&cached_percpu_stats, cpu);
> + val = cached_bstat->cputime.utime;
> + do_div(val, NSEC_PER_USEC);
> + seq_printf(seq, " %llu", val);
> + }
> + seq_puts(seq, "\n");
> +
> + seq_puts(seq, "system_usec");
> + for_each_possible_cpu(cpu) {
> + cached_bstat = per_cpu_ptr(&cached_percpu_stats, cpu);
> + val = cached_bstat->cputime.stime;
> + do_div(val, NSEC_PER_USEC);
> + seq_printf(seq, " %llu", val);
> + }
> + seq_puts(seq, "\n");
This is an anti-pattern; given enough CPUs (easy) this will trivially
overflow the 1 page seq buffer.
People are already struggling to fix existing ABI, lets not make the
problem worse.
next prev parent reply other threads:[~2022-01-11 12:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-07 23:41 Josh Don
2022-01-07 23:41 ` [PATCH 2/2] sched: show percpu throttled stats Josh Don
2022-01-11 12:49 ` Peter Zijlstra [this message]
2022-01-11 23:38 ` [PATCH 1/2] cgroup: add cpu.stat_percpu Josh Don
2022-01-12 8:30 ` Peter Zijlstra
2022-01-12 20:23 ` Tejun Heo
2022-01-13 1:55 ` Josh Don
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