From: Tejun Heo <tj@kernel.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Shaohua Li <shaohua.li@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"cl@linux.com" <cl@linux.com>,
"npiggin@kernel.dk" <npiggin@kernel.dk>
Subject: Re: [patch V3] percpu_counter: scalability works
Date: Tue, 17 May 2011 11:11:02 +0200 [thread overview]
Message-ID: <20110517091102.GE20624@htj.dyndns.org> (raw)
In-Reply-To: <1305622861.2850.21.camel@edumazet-laptop>
Hello, Eric, Shaohua.
On Tue, May 17, 2011 at 11:01:01AM +0200, Eric Dumazet wrote:
> Just convince him that percpu_counter by itself cannot bring a max
> deviation guarantee. No percpu_counter user cares at all. If they do,
> then percpu_counter choice for their implementation is probably wrong.
>
> [ We dont provide yet a percpu_counter_add_return() function ]
I haven't gone through this thread yet but will do so later today, but
let me clarify the whole deviation thing.
1. I don't care reasonable (can't think of a better word at the
moment) level of deviation. Under high level of concurrency, the
exact value isn't even well defined - nobody can tell operations
happened in what order anyway.
2. But I _do_ object to _sum() has the possibility of deviating by
multiples of @batch even with very low level of activity.
I'm completely fine with #1. I'm not that crazy but I don't really
want to take #2 - that makes the whole _sum() interface almost
pointless. Also, I don't want to add big honking lglock to just avoid
#2 unless it can be shown that the same effect can't be achieved in
saner manner and I'm highly skeptical that would happen.
Thank you.
--
tejun
next prev parent reply other threads:[~2011-05-17 9:11 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-11 8:10 [patch v2 0/5] percpu_counter: bug fix and enhancement Shaohua Li
2011-05-11 8:10 ` [patch v2 1/5] percpu_counter: fix code for 32bit systems for UP Shaohua Li
2011-05-11 8:10 ` [patch v2 2/5] lglock: convert it to work with dynamically allocated structure Shaohua Li
2011-05-11 8:10 ` [patch v2 3/5] percpu_counter: use lglock to protect percpu data Shaohua Li
2011-05-11 8:10 ` [patch v2 4/5] percpu_counter: use atomic64 for counter in SMP Shaohua Li
2011-05-11 9:34 ` Andrew Morton
2011-05-12 2:40 ` Shaohua Li
2011-05-11 8:10 ` [patch v2 5/5] percpu_counter: preemptless __per_cpu_counter_add Shaohua Li
2011-05-11 9:28 ` [patch v2 0/5] percpu_counter: bug fix and enhancement Tejun Heo
2011-05-12 2:48 ` Shaohua Li
2011-05-12 8:21 ` Tejun Heo
2011-05-12 8:55 ` Shaohua Li
2011-05-12 8:59 ` Tejun Heo
2011-05-12 9:02 ` Eric Dumazet
2011-05-12 9:03 ` Eric Dumazet
2011-05-12 9:05 ` Tejun Heo
2011-05-13 3:09 ` Shaohua Li
2011-05-13 4:37 ` Shaohua Li
2011-05-13 5:20 ` Eric Dumazet
2011-05-13 5:28 ` Shaohua Li
2011-05-13 6:34 ` Eric Dumazet
2011-05-13 7:33 ` Shaohua Li
2011-05-13 14:51 ` [patch] percpu_counter: scalability works Eric Dumazet
2011-05-13 15:39 ` Eric Dumazet
2011-05-13 16:35 ` [patch V2] " Eric Dumazet
2011-05-13 16:46 ` Eric Dumazet
2011-05-13 22:03 ` [patch V3] " Eric Dumazet
2011-05-16 0:58 ` Shaohua Li
2011-05-16 6:11 ` Eric Dumazet
2011-05-16 6:37 ` Shaohua Li
2011-05-16 6:55 ` Eric Dumazet
2011-05-16 7:15 ` Shaohua Li
2011-05-16 7:44 ` Eric Dumazet
2011-05-16 8:34 ` Shaohua Li
2011-05-16 9:35 ` Eric Dumazet
2011-05-16 14:22 ` Eric Dumazet
2011-05-17 0:55 ` Shaohua Li
2011-05-17 4:56 ` Eric Dumazet
2011-05-17 5:22 ` Shaohua Li
2011-05-17 9:01 ` Eric Dumazet
2011-05-17 9:11 ` Tejun Heo [this message]
2011-05-17 9:45 ` Eric Dumazet
2011-05-17 9:50 ` Tejun Heo
2011-05-17 12:20 ` Eric Dumazet
2011-05-17 12:45 ` Tejun Heo
2011-05-17 13:00 ` Eric Dumazet
2011-05-17 13:04 ` Tejun Heo
2011-05-17 13:55 ` Christoph Lameter
2011-05-17 14:02 ` Tejun Heo
2011-05-17 14:38 ` Christoph Lameter
2011-05-18 1:00 ` Shaohua Li
2011-05-12 14:38 ` [patch v2 0/5] percpu_counter: bug fix and enhancement Christoph Lameter
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