From: Khalid Aziz <khalid.aziz@oracle.com>
To: David Lang <david@lang.hm>
Cc: Oleg Nesterov <oleg@redhat.com>, Andi Kleen <andi@firstfloor.org>,
Thomas Gleixner <tglx@linutronix.de>,
One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
peterz@infradead.org, akpm@linux-foundation.org,
viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [RFC] [PATCH] Pre-emption control for userspace
Date: Wed, 05 Mar 2014 17:17:24 -0700 [thread overview]
Message-ID: <5317BE94.20703@oracle.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1403051555360.6682@nftneq.ynat.uz>
On 03/05/2014 04:59 PM, David Lang wrote:
> what's the cost to setup mmap of this file in /proc. this is sounding
> like a lot of work.
That is a one time cost paid when a thread initializes itself.
>
>>> is this gain from not giving up the CPU at all? or is it from avoiding
>>> all the delays due to the contending thread trying in turn? the
>>> yield_to() approach avoids all those other threads trying in turn so it
>>> should get fairly close to the same benefits.
>>>
>>
>> The gain is from avoiding contention by giving locking thread a chance
>> to complete its critical section which is expected to be very short
>> (certainly shorter than timeslice). Pre-emption immunity gives it one
>> and only one additional timeslice.
>
> but the yield_to() does almost the same thing, there is a small bump,
> but you don't have to wait for thread B to spin, thread C..ZZZ etc to
> spin before thread A can finish it's work. As soon as the second thread
> hits the critical section, thread A is going to be able to do more work
> (and hopefully finish)
>
>> Hope this helps clear things up.
>
> It doesn't sound like you and I are understanding how the yield_to()
> approach would work. I hope my comments have helped get us on the same
> page.
>
I apologize if I am being dense. My understanding of yield_to() is what
Oleg had said in his reply earlier, so I will quote the example he gave:
my_lock()
{
if (!TRY_LOCK()) {
yield_to(owner);
LOCK();
}
owner = gettid();
}
If thread A had already lost the processor by the time thread B executes
above code, wouldn't we have paid the price of two context switches for
thread A?
Thanks,
Khalid
next prev parent reply other threads:[~2014-03-06 0:18 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-03 18:07 [RFC] [PATCH] Pre-emption control for userspace Khalid Aziz
2014-03-03 21:51 ` Davidlohr Bueso
2014-03-03 23:29 ` Khalid Aziz
2014-03-04 13:56 ` Oleg Nesterov
2014-03-04 17:44 ` Khalid Aziz
2014-03-04 18:38 ` Al Viro
2014-03-04 19:01 ` Khalid Aziz
2014-03-04 19:03 ` Oleg Nesterov
2014-03-04 20:14 ` Khalid Aziz
2014-03-05 14:38 ` Oleg Nesterov
2014-03-05 16:12 ` Oleg Nesterov
2014-03-05 17:10 ` Khalid Aziz
2014-03-04 21:12 ` H. Peter Anvin
2014-03-04 21:39 ` Khalid Aziz
2014-03-04 22:23 ` One Thousand Gnomes
2014-03-04 22:44 ` Khalid Aziz
2014-03-05 0:39 ` Thomas Gleixner
2014-03-05 0:51 ` Andi Kleen
2014-03-05 11:10 ` Peter Zijlstra
2014-03-05 17:29 ` Khalid Aziz
2014-03-05 19:58 ` Khalid Aziz
2014-03-06 9:57 ` Peter Zijlstra
2014-03-06 16:08 ` Khalid Aziz
2014-03-06 11:14 ` Thomas Gleixner
2014-03-06 16:32 ` Khalid Aziz
2014-03-05 14:54 ` Oleg Nesterov
2014-03-05 15:56 ` Andi Kleen
2014-03-05 16:36 ` Oleg Nesterov
2014-03-05 17:22 ` Khalid Aziz
2014-03-05 23:13 ` David Lang
2014-03-05 23:48 ` Khalid Aziz
2014-03-05 23:56 ` H. Peter Anvin
2014-03-06 0:02 ` Khalid Aziz
2014-03-06 0:13 ` H. Peter Anvin
2014-03-05 23:59 ` David Lang
2014-03-06 0:17 ` Khalid Aziz [this message]
2014-03-06 0:36 ` David Lang
2014-03-06 1:22 ` Khalid Aziz
2014-03-06 14:23 ` David Lang
2014-03-06 12:13 ` Kevin Easton
2014-03-06 13:59 ` Peter Zijlstra
2014-03-06 22:41 ` Andi Kleen
2014-03-06 14:25 ` David Lang
2014-03-06 16:12 ` Khalid Aziz
2014-03-06 13:24 ` Rasmus Villemoes
2014-03-06 13:34 ` Peter Zijlstra
2014-03-06 13:45 ` Rasmus Villemoes
2014-03-06 14:02 ` Peter Zijlstra
2014-03-06 14:33 ` Thomas Gleixner
2014-03-06 14:34 ` H. Peter Anvin
2014-03-06 14:04 ` Thomas Gleixner
2014-03-25 17:17 ` [PATCH v2] " Khalid Aziz
2014-03-25 17:44 ` Andrew Morton
2014-03-25 17:56 ` Khalid Aziz
2014-03-25 18:14 ` Andrew Morton
2014-03-25 17:46 ` Oleg Nesterov
2014-03-25 17:59 ` Khalid Aziz
2014-03-25 18:20 ` Andi Kleen
2014-03-25 18:47 ` Khalid Aziz
2014-03-25 19:47 ` Andi Kleen
2014-03-25 18:59 ` Eric W. Biederman
2014-03-25 19:15 ` Khalid Aziz
2014-03-25 20:31 ` Eric W. Biederman
2014-03-25 21:37 ` Khalid Aziz
2014-03-26 6:03 ` Mike Galbraith
2014-03-25 23:01 ` [RFC] [PATCH] " Davidlohr Bueso
2014-03-25 23:29 ` Khalid Aziz
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