Messages in this thread | | | Subject | Re: [PATCH v4] sched/debug: Use sched_debug_lock to serialize use of cgroup_path[] only | From | Waiman Long <> | Date | Mon, 5 Apr 2021 21:57:07 -0400 |
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On 4/5/21 8:18 PM, Steven Rostedt wrote: > On Mon, 5 Apr 2021 19:42:03 -0400 > Waiman Long <longman@redhat.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. > This patch is actually inspired by your suggestion, though it is structured differently from your approach. I really want to thank you for your valuable feedback.
I realized that printing to a sequence file wasn't really a problem, only printing to console can be problematic. That is why I decided to allow unlimited use of group_path[] for those users and only one console writer is allowed to use it. As for calling touch_nmi_watchdog(), I am still thinking where will be the right place to do it, but it can be done with a separate patch, if needed.
Cheers, Longman
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