All of lore.kernel.org
 help / color / mirror / Atom feed
From: Avi Kivity <avi@scylladb.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: maged michael <maged.michael@gmail.com>,
	Andrew Hunter <ahh@google.com>, gromer <gromer@google.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: Udpated sys_membarrier() speedup patch, FYI
Date: Mon, 31 Jul 2017 09:03:09 +0300	[thread overview]
Message-ID: <f3078a0e-0f2b-c773-228f-988087d0561a@scylladb.com> (raw)
In-Reply-To: <1546253326.29115.1501189344518.JavaMail.zimbra@efficios.com>



On 07/28/2017 12:02 AM, Mathieu Desnoyers wrote:
> ----- On Jul 27, 2017, at 4:58 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
>
>> ----- On Jul 27, 2017, at 4:37 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com
>> wrote:
>>
>>> On Thu, Jul 27, 2017 at 11:04:13PM +0300, Avi Kivity wrote:
> [...]
>>>>> +
>>>>> +	this_cpu = raw_smp_processor_id();
>>>>> +	for_each_online_cpu(cpu) {
>>>>> +		struct task_struct *p;
>>>>> +
>>>>> +		if (cpu == this_cpu)
>>>>> +			continue;
>>>>> +		rcu_read_lock();
>>>>> +		p = task_rcu_dereference(&cpu_rq(cpu)->curr);
>>>>> +		if (p && p->mm == current->mm)
>>>>> +			__cpumask_set_cpu(cpu, tmpmask);
>>>> This gets you some false positives, if the CPU idled then mm will
>>>> not have changed.
>>> Good point!  The battery-powered embedded guys would probably prefer
>>> we not needlessly IPI idle CPUs.  We cannot rely on RCU's dyntick-idle
>>> state in nohz_full cases.  Not sure if is_idle_task() can be used
>>> safely, given things like play_idle().
>> Would changing the check in this loop to:
>>
>> if (p && !is_idle_task(p) && p->mm == current->mm) {
>>
>> work for you ?
> Avi, is there an optimization that allows current->mm to be non-null
> when the idle task is scheduled that I am missing ?
>
> I would have expected current->mm to be always NULL for idle
> tasks.
>
>

I remembered that current->mm does not change when switching to a kernel 
task, but my Kernlish is very rusty, or maybe it has changed.

  reply	other threads:[~2017-07-31  6:03 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-27 18:12 Udpated sys_membarrier() speedup patch, FYI Paul E. McKenney
2017-07-27 18:36 ` Andrew Hunter
2017-07-27 19:06   ` Paul E. McKenney
2017-07-28 17:37     ` Andrew Hunter
2017-07-28 18:14       ` Paul E. McKenney
2017-07-27 19:20 ` Avi Kivity
2017-07-27 19:43   ` Paul E. McKenney
2017-07-27 20:04     ` Avi Kivity
2017-07-27 20:37       ` Paul E. McKenney
2017-07-27 20:58         ` Mathieu Desnoyers
2017-07-27 21:02           ` Mathieu Desnoyers
2017-07-31  6:03             ` Avi Kivity [this message]
2017-07-31  8:37               ` Peter Zijlstra
2017-07-31  8:53                 ` Avi Kivity
2017-07-28 17:15     ` Andrew Hunter
2017-07-28 17:25       ` Mathieu Desnoyers
2017-07-28 17:31       ` Paul E. McKenney
2017-07-28 17:48         ` Mathieu Desnoyers
2017-07-31 18:00 ` Dave Watson
2017-07-31 18:27   ` Paul E. McKenney

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=f3078a0e-0f2b-c773-228f-988087d0561a@scylladb.com \
    --to=avi@scylladb.com \
    --cc=ahh@google.com \
    --cc=gromer@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=maged.michael@gmail.com \
    --cc=mathieu.desnoyers@efficios.com \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.