From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Rusty Russell <rusty@rustcorp.com.au>,
Nick Piggin <npiggin@kernel.dk>,
linux-kernel <linux-kernel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andi Kleen <ak@linux.intel.com>,
linux-fsdevel@vger.kernel.org,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Arjan van de Ven <arjan.van.de.ven@intel.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
mc@linux.vnet.ibm.com
Subject: Re: [PATCH] cpumask: fix lg_lock/br_lock.
Date: Thu, 01 Mar 2012 15:26:26 +0530 [thread overview]
Message-ID: <4F4F47CA.2060900@linux.vnet.ibm.com> (raw)
In-Reply-To: <20120301094529.GA366@elte.hu>
On 03/01/2012 03:15 PM, Ingo Molnar wrote:
>
> * Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>
>> We wanted to avoid doing for_each_possible_cpu() to avoid the
>> unnecessary performance hit. [...]
>
> That was done at the cost of making the code rather complex.
>
Sadly, yes..
> The thing is, *ANY* cpu-mask loop is an utter slowpath, so the
> "performance hit" is an overstatement. There's already dozens of
> of for_each_possible_cpu() loops in the kernel, and it's a
> perfectly acceptable solution in such cases.
>
> I suspect it does not matter much now as the code appears to be
> correct, but in general we want to opt for simpler designs for
> rare and fragile codepaths.
>
Ok, makes sense. And now looking back at the amount of complexity
we built into this just to avoid the for_each_possible_cpu() loop,
I wonder why we went to such lengths at all! (considering what you
said above about any cpu-mask loop..)
Regards,
Srivatsa S. Bhat
next prev parent reply other threads:[~2012-03-01 9:56 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-27 23:22 [PATCH] cpumask: fix lg_lock/br_lock Rusty Russell
2012-02-27 23:53 ` Andrew Morton
2012-02-28 8:43 ` Ingo Molnar
2012-02-28 11:25 ` Andi Kleen
2012-02-28 12:51 ` Ingo Molnar
2012-02-28 21:27 ` Andrew Morton
2012-02-29 5:44 ` Srivatsa S. Bhat
2012-02-29 9:17 ` Ingo Molnar
2012-02-29 11:12 ` Srivatsa S. Bhat
2012-03-01 7:38 ` Ingo Molnar
2012-03-01 9:15 ` Srivatsa S. Bhat
2012-03-01 9:45 ` Ingo Molnar
2012-03-01 9:56 ` Srivatsa S. Bhat [this message]
2012-03-01 8:12 ` Srivatsa S. Bhat
2012-03-01 8:15 ` [PATCH 1/3] CPU hotplug: Fix issues with callback registration Srivatsa S. Bhat
2012-03-01 8:16 ` [PATCH 2/3] CPU hotplug, arch/powerpc: Fix CPU hotplug " Srivatsa S. Bhat
2012-03-01 8:18 ` [PATCH 3/3] CPU hotplug, arch/sparc: " Srivatsa S. Bhat
2012-02-29 8:29 ` [PATCH] cpumask: fix lg_lock/br_lock Ingo Molnar
2012-02-29 8:58 ` Peter Zijlstra
2012-02-29 9:32 ` Ingo Molnar
2012-02-28 11:24 ` Andi Kleen
2012-03-05 7:02 ` Rusty Russell
2012-03-05 7:03 ` [PATCH 1/3] lglock: remove online variants of lock Rusty Russell
2012-04-20 11:12 ` Nick Piggin
2012-03-05 7:04 ` [PATCH 2/3] brlocks/lglocks: API cleanups Rusty Russell
2012-03-05 7:05 ` [PATCH 3/3] brlocks/lglocks: turn into functions Rusty Russell
2012-04-20 11:21 ` Nick Piggin
2012-05-07 3:39 ` Rusty Russell
2012-05-07 5:46 ` Al Viro
2012-05-08 3:59 ` [PATCH 1/3] lglock: remove online variants of lock Rusty Russell
2012-05-08 4:50 ` Al Viro
2012-05-08 6:12 ` Rusty Russell
2012-05-08 4:02 ` [PATCH 2/3] brlocks/lglocks: API cleanups Rusty Russell
2012-05-08 4:02 ` [PATCH 3/3] brlocks/lglocks: turn into functions Rusty Russell
2012-05-09 7:35 ` Nick Piggin
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