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Date: Mon, 5 Apr 2021 20:18:07 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Waiman Long <longman@...hat.com> Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira <bristot@...hat.com>, Bharata B Rao <bharata@...ux.vnet.ibm.com>, Phil Auld <pauld@...hat.com>, Daniel Thompson <daniel.thompson@...aro.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v4] sched/debug: Use sched_debug_lock to serialize use of cgroup_path[] only On Mon, 5 Apr 2021 19:42:03 -0400 Waiman Long <longman@...hat.com> wrote: > +/* > + * All the print_cpu() callers from sched_debug_show() will be allowed > + * to contend for sched_debug_lock and use group_path[] as their SEQ_printf() > + * calls will be much faster. However only one print_cpu() caller from > + * sysrq_sched_debug_show() which outputs to the console will be allowed > + * to use group_path[]. Another parallel console writer will have to use > + * a shorter stack buffer instead. Since the console output will be garbled > + * anyway, truncation of some cgroup paths shouldn't be a big issue. > + */ > +#define SEQ_printf_task_group_path(m, tg, fmt...) \ > +{ \ > + unsigned long flags; \ > + int token = m ? TOKEN_NA \ > + : xchg_acquire(&console_token, TOKEN_NONE); \ > + \ > + if (token == TOKEN_NONE) { \ > + char buf[128]; \ > + task_group_path(tg, buf, sizeof(buf)); \ > + SEQ_printf(m, fmt, buf); \ > + } else { \ > + spin_lock_irqsave(&sched_debug_lock, flags); \ > + task_group_path(tg, group_path, sizeof(group_path)); \ > + SEQ_printf(m, fmt, group_path); \ > + spin_unlock_irqrestore(&sched_debug_lock, flags); \ > + if (token == TOKEN_ACQUIRED) \ > + smp_store_release(&console_token, token); \ > + } \ > } > #endif And you said my suggestion was complex! I'll let others review this. -- Steve
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