linux-kernel - Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 1 Oct 2013 17:56:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Fernando Luis Vázquez Cao 
	<fernando_b1@....ntt.co.jp>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock


So what's wrong with something like:

struct cpu_idletime {
       seqlock_t seqlock;
       unsigned long nr_iowait;
       u64 start;
       u64 idle_time,
       u64 iowait_time,
} __cacheline_aligned_in_smp;

DEFINE_PER_CPU(struct cpu_idletime, cpu_idletime);

void io_schedule(void)
{
	struct cpu_idletime *it = __raw_get_cpu_var(cpu_idletime);

	write_seqlock(&it->seqlock);
	if (!it->nr_iowait++)
		it->start = local_clock();
	write_sequnlock(&it->seqlock);

	current->in_iowait = 1;
	schedule();
	current->in_iowait = 0;

	write_seqlock(&it->seqlock);
	if (!--it->nr_iowait)
		it->iowait_time += local_clock() - it->start;
	write_sequnlock(&it->seqlock);
}

Afaict you don't need the preempt disable and atomic muck at all.

It will all get a little more complicated to deal with overlapping idle
and iowait times, but the idea is the same.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/